In order to further explore the influence of physical coverage on still water evaporation from water surface in arid zone plain reservoir, the experiment selected the black PE floating balls with a diameter of 100 mm as the cover material, and two 1m2 area of the square tin trunk were selected as evaporator (A evaporator and B evaporator). The A evaporator is completely covered with floating balls from the water surface (the coverage rate is 86%), and B is not covered. Through the comparison test of A and B evaporators, the inhibition rate of the floating balls to the water surface of the evaporator is 83.8%. When the arid zone plain reservoir were largely covered by the floating balls (the coverage rate is close to 91%), the inhibition rate of the floating balls to the surface of the water can reach 89.6%.