Water is the important resource to guarantee the existence and development of oases in arid areas.To improve the utilization efficiency of water resources in Manas River Basin,this paper investigated the trends and periods of runoff based on the runoff and climate data for the past 50 years.Subsequently,with the socioeconomic and water resources data,we studied a comprehensive evaluation on the water security in this area.The results indicated that the stream flows in the three hydrological stations of Hongshanzui,Kensiwat and Bajiahu have significantly increased and undergone abrupt changes,with periods of 18 and 20 years.According to assessment,water security in the Manas River Basin was at an unsafe level in 2008.In criterion layer,the ecological security index and the index of supply-demand situation are both at the relatively secure level; the quantity index and socioeconomic index of water resources are at the unsafe level and basic security level,respectively.Therefore,in order to achieve sustainable economic and social development within the Manas River Basin,it is vital to take a series of effective measures to improve the status of water security.