Based on the data two-times a day in 1980-1991 for the Duchang evaporation-station, the differences of water-surface evaporation and discount coefficient between day and night for small type evaporation pan are analyzed and comparisons with that for the E₆₀₁-type evaporation pan are also made. Moreover, features and existing questions of water surface. evaporation for the small-type evaporation pan are revealed,and improving suggestions are also proposed.