This paper measured the evapotranspiration (ET) rate of a winter wheat field on the Loess Plateau tableland by using large-scale weighing lysimeter, and analyzed the effects of wheat leaf area index (LAI) , soil water content, air temperature, and rainfall on the ET at the time scales of growth stage, month, day, and hour. The results showed that the mean daily ET rate in different growth stages was in the order of booting-heading > flowering > erecting > jointing > filling > reviving > ripening > overwintering. Air temperature had a larger effect in initial stage, LAI was in mid stage, and soil water content was in last stage in the experimental year. The mean daily ET rate was markedly decreased from 6.25 mmn x d(-1) at booting-heading stage to 2.66 mm x d(-1) at grain-filling stage due to soil water deficit. The monthly ET rate in April, May and June was higher than that in other months, and the ET amount of the three months accounted for 80% of the total during the experimental period. The apices of daily ET curve mainly reflected the effects of rainfall, and the hourly ET process basically reflected the ET changes with weather conditions.