Abstract: The evaporation losses from plain reservoirs are significant in arid area due to shallow water depth, high wind speed, high temperature and relatively low air humidity. Therefore, we conducted a series of tests for a year to reduce the water surface evaporation from the reservoir which was built for third-stage soil and water conservation in Turpan Xinjiang. During the tests, the reservoir was covered by magnetic and non-magnetic floating plates. Also, we analyzed the water saving efficiency of the magnetic and non-magnetic floating plates in the case of the same coverage area. The results show that under the same meteorological conditions, when the single magnetic floating plate covered 25%, 50% and 70% of the reservoir surface, the evaporation inhibition rate was 27.4%, 41.5% and 59.1% respectively. When the non-magnetic floating plates covered 25%, 50% and 70% of the reservoir surface, the evaporation inhibition rate were 22.1%, 38.1% and 57.3% respectively. The evaporation inhibition rate of the magnetic floating plate increased by 5.3%, 3.4% and 1.8% respectively, compared with non-magnetic floating plate. In conclusion, the magnetic floating plate could be more effective in water saving, which is significant to improving water resources use efficiency of plain reservoirs in arid area.