We conducted two campaigns to study total mercury (THg) and methyl mercury (MeHg) in water bodies of Xiaolangdi reservoir, which were constructed in 2001 and drained for desilification in early June every year. The first campaign was conducted in May 2010 and 7 sampling sites were selected from upstream to the dam. The second campaign was conducted in Nov. 2010 and 3 sampling sites were selected in Nov.2010. Our results showed that the average THg(30.5ng/L) concentration of water bodies in main channel of xiaolangdi reservoir was higher that of in tributary (19.3ng/L) and declined from upstream to downstream water body. Drainage of reservoir could decline mercury in water and water residence time was an important variable affecting mercury accumulation. The MeHg concentration had the same trend compared to THg from upstream to downstream water bodies. Mingzhudao, luoyu and dam water bodies were 0.045ng/L, 0.039ng/L and 0.037ng/L water bodies, respectively.