Gun Nuur(50°15N,106°36E,600 m a.s.l.) is a closed depressing basin situated in the east of the OrhonSelenga depression with semi-saline to fresh water and flat bottom,an eutrophic water with pH 8,and the maximum of water depth is 5 m.The lake area is 2.5 km~2.The lake is closed most of time and almost completely isolated from the Buryn Gol River,the right-hand tributary of the Orhon River.Atmospheric precipitation and ground waters are the main alimentation sources of the lake.We drilled lake core GUN2004-A at Gun Nuur(50°15’39.8 “N,106°36’58” E,605 m a.s.l,490 cm water depth) on August,2004.Lithology characteristic is described as following:0~90 cm dark grey lake mud;90~190 cm grey-brown mud;190~320 cm grey-brown laminated mud,and it is dark grey clay including a lot of mollusks between 260 cm to 270 cm interval;320~330 cm grey black muddy silt;330~370 cm black-brown mud;370~386 cm grey-black mud silt;386~398 cm dark grey mud;398~440 cm grey black muddy silt;440~792cm brown-yellow laminated carbonate mud;792~816 cm grey black slity mud;816~835 cm grey black silt to fine sand;835~870 cm brown-black silt;870~928 cm grey silt to sand.The age model is constructed on 39 AMS ~(14)C dates.The ~(14)C date at the top(surface) of the core Gun 2002 indicates that the carbon reservoir effect in the Gun Nuur Lake is about 1200 years with an assumption that this carbon reservoir effect applies to the entire Holocene.Multi-proxies paleoenvironmental reconstruction is used in this core.As the analyzed grain size,TOC,CaCO_3-content,δ~(13) C and δ~(18)O of bulk carbonate,susceptibility and x_(fd),we can conclude that oxygen isotope of bulk carbonate is controlled by the temperature,effective humidity and the water residence time together.By the grain size parameter,we distinguish some aeolian deposition layers since late-glacial this area.By the multi-proxies researching,lake level changes can be known:~10340 cal a BP,6680~5890 cal a BP,4950~4300 cal a BP,3440~2750 cal a BP these 4 stages were cold and dry periods with low lake level characteristics.10340~6680 cal a BP,was the highest lake level period.5890~4950 cal a BP,4300~3440,2750~1780 cal a BP were the warm and wet periods with a high lake level.After 1780~ cal a BP,temperature decreased but lake level changed from high to intermediate in the closed lake,δ~(13) C and δ~(18) O of bulk carbonate changed heavier and heavier with the long residence time.The climate changed cold and wet since about 1780 cal a BP standing for westerlies-dominate. Gun Nuur (50 ° 15N, 106 ° 36E, 600 m asl) is a closed depressing basin situated in the east of the OrhonSelenga depression with semi-saline to fresh water and flat bottom, an eutrophic water with pH 8, and the maximum of The lake area is 2.5 km ~ 2. The lake is closed most of time and almost completely isolated from the Buryn Gol River, the right-hand tributary of the Orhon River. Atmospheric precipitation and ground waters are the main alimentation sources of the lake. We drilled lake core GUN2004-A at Gun Nuur (50 ° 15’39.8 “N, 106 ° 36’58” E, 605 m asl, 490 cm water depth) on August, 2004. Theory The characteristic is described as follows: 0 to 90 cm dark gray lake mud; 90 to 190 cm gray-brown mud; and 190 to 320 cm gray-brown laminated mud, and it is dark gray clay including a lot of mollusks between 260 cm to 270 cm interval; 320-330 cm gray black muddy silt; 330-370 cm black-brown mud; 370-386 cm gray-black mud silt; 386-398 cm dark gray mud; 792cm brown-yell 839-880 cm brown-black silt; 870-928 cm gray silt to sand. The age model is constructed on 39 C date at the top (surface) of the core Gun 2002 indicates that the carbon reservoir effect in the Gun Nuur Lake is about 1200 years with an assumption that this carbon reservoir effect applies to the entire Holocene. Multi-proxies paleoenvironmental reconstruction is used in this core. As the analyzed grain size, TOC, CaCO 3 -content, δ ~ (13) C and δ ~ (18) O of bulk carbonate, ), we can conclude that oxygen isotope of bulk carbonate is controlled by the temperature, effective humidity and the water residence time together.By the grain size parameter, we distinguish some aeolian deposition layers since late-glacial this area.By the multi-proxies researching, lake level changes can be known: ~ 10340 cal a BP, 6680 ~ 5890 cal a BP, 4950 ~ 4300 cal a BP, 3440 ~ 2750 cal a BP these4 stages were cold and dry periods with low lake level characteristics.10340 ~ 6680 cal a BP, was the highest lake level period.5890 ~ ​​4950 cal a BP, 4300 ~ 3440,2750 ~ 1780 cal a BP were the warm and wet periods with a high lake level. After 1780 ~ cal a BP, temperature decreased but lake level changed from high to intermediate in the closed lake, δ ~ (13) C and δ ~ (18) O of bulk carbonate shifted heavier and heavier with the long residence time. The climate changed cold and wet since about 1780 cal a BP standing for westerlies-dominate.