Palaeohydrological investigations were carried out in the Guchuan Basin in the upper reaches of the Weihe River valley, China. A set of palaeoflood slackwater deposits(SWDs) was found interbedded in the Holocene loess-paleosol sequence at the Guchuanzhen site(GCZ). These palaeoflood SWDs were studied by field observations and laboratory analyses including concentrations of chemical elements and optically stimulated luminescence(OSL) dating. The results showed that the palaeoflood SWDs were the result of the secondary separations of the surface soil and weathered soil layers during the process of water transport and deposition, and without obvious weathering during soil development. These extraordinary flood events were dated back to 3,200-3,000 a B.P. with the OSL method and checked by archaeological dating of the human remains retrieved from the profile. These extraordinary flood events were therefore considered as regional expression of known climatic events and demonstrated the climatic instability in the Holocene. This result is important for understanding the effects of global climate change on the dynamics of river systems. Palaeohydrological investigations were carried out in the Guchuan Basin in the upper reaches of the Weihe River valley, China. A set of palaeoflood slackwater deposits (SWDs) was found interbedded in the Holocene loess-paleosol sequence at the Guchuanzhen site (GCZ). These palaeoflood SWDs were studied by field observations and laboratory analyzes including concentrations of chemical elements and optically stimulated luminescence (OSL) dating. The results showed that the palaeoflood SWDs were the result of the secondary separations of the surface soil and weathered soil layers during the process of water transport and deposition, and without obvious weathering during soil development. These extraordinary flood events were dated back to 3,200-3,000 a BP with the OSL method and checked by archaeological dating of the human remains retrieved from the profile. as regional expression of known climatic events and demonstrated the clim atic instability in the Holocene. This result is important for understanding the effects of global climate change on the dynamics of river systems.