Based on the experiment on plots, impacts of grass coverage change on runoff and sediment yield in the Tianchi Lake Natural Reserve Area in Xinjiang were investigated. Grass coverage had much more influence on sediment yield than that on runoff. Total runoff depth for 35% grass coverage was 1.4 , 1.5 , and 2.2 times that for 50 % , 55 %, and 75 % grass cover degrees, and total sediment yield for 35 % grass coverage was 4, 6, and 10 times that for 50 %, 55 %, and 75 % grass cover degrees, respectively. The relations of grass coverage to total runoff and sediment yield can be described by exponential function. Rainfall intensity had much more influence on sediment yield than runoff. In the same condition of grass coverage, runoff and sediment yield were increased with increased rainfall intensity. The relation of rainfall intensity to total runoff and sediment yield can be described by binomial function. The relation between grass coverage and total runoff depth can be described by exponential function.