Abstract: A field experiment was conducted in a banana-cultivation screenhouse to study the change and relationship between crop evapotranspiration and reference crop evapotranspiration (ET0). The effects of microclimatic factors inside the screenhouse on ET0 were also analyzed. Results show that ET0 and Class-A pan-evaporation inside the screenhouse respectively decrease by 39% and 42% in comparison with those in the open field. Also, banana transpiration in the screenhouse decreases by 53% in comparison with those in the open field. Reductions in banana transpiration, ET0 and pan-evaporation inside the screenhouse are mainly due to the decreases in net radiation and wind speed. Air temperature and vapor pressure, on the other hand, exert a minimal reduction effect on ET0. A regression relation exists between screenhouse and open-field ET0 and pan-evaporation. The statistical Class-A pan-coefficient for the study area is 0.84.