Abstract: Based on the improvements of observing methods in 1980-1981,the evapotranspiration experiment in a tropical monsoon forest was conducted using EBBR method on Hainan Island from 1983 to 1985 during which 49 sampled days in dry seasons and rainy seasons were selected at random.A stepwise multiple regression was set up using the daily evapotranspiration values and the synoptic data which were recorded daily from a meteorological station 1 km away from the Research Station of Tropical Forestry.The rainfall was taken into consideration in the regession equations by using especially designed index "Available Water for Evaporation" (AWE).As comparison,the every day EPT values were calculated using Penman-Monteith equation.The computed results turned to be 534.7mm,520.7mm and 564.0 mm according to EBBR method; and 721.1 mm,714.8 and 728.4 mm according to Penman-Monteith equation for 1983,1984 and 1985 respectively.The EPT/rainfall ratios were 30.4% 30.2% and 44.9% with EBBR method; and 41.0%,41.5% and 58.0% with Penman-Moneith equation for 1983,1984 and 1985 respectively.The ratios were strongly correlated with intensities of rainfall.The larger the intensities of rainfall,the smaller the rater consumption percent (EPT/rainfall) because of the greater runoff.The minimun average daily EPT values were 0.36 mm/d and 0.49mm/d by the two methods respectively; and the corresponding maximum average daily EPT values were 2.55mm/d and 3.14mm/d respectively.