In order to the feasibility of inhibiting evaporation in plain reservoirs of arid area water inhibit by physics technology,the paper used PVC foam floating plate as covering material of water.It connected floating slabs into the required different areas and then recorded floating slabs' working situations when they freely floated on experiment area.Taking the wetting rate of floating slabs under the influence of wind speed as a variable,the paper collected the statistics of the wind speed in experimental period and the wetting rates each floating slab under different wind speed so as figure out the evaporation preventing rate of floating slab of different scales in the experiment period.The results showed that when the floating plate area increases from 1 m2 to 16 m2, its average evaporation inhibition rate increases from 74% to 88.3%, which proved the feasibility of a large area covering the reservoir surface so as to inhibit water evaporation.The technique can lay theoretical foundation for the northwest arid area plain reservoirs to early realize the water engineering measures of surface evaporation inhibited by physical technique.