To understand the heavy metal mercury levels in the surface water of Lake Ulansuhai, samples were collected in January 2011. The total mercury concentration was analyzed. Distribution characteristics, pollution levels and health risk assessment were revealed by GIS, Pollution Evaluation Index and Health Risk Assessment Model. The average mercury concentrations in surface lake water were 1.04 μg/L, indicating a relatively high content of mercury. All sampling contents were beyond the first surface water standards and national fisheries standards, and 50% samples were beyond the fourth surface water standards. The high mercury concentrations at the inlet of the lake, while the low concentrations at the outlet of the lake. Considering the health risk caused by non-carcinogen in the water, the risk levels ranged from 0.75×10^-9 to 2.15×10^-9 a^-1. The contribution rate of mercury is 71.43% -92.44%. The mercury pollution and risk is high and should pay more attention on that.