Using the weighing instrument—hydraulic evapotranspirometer, we
have researched evapotranspiration of spring wheat in different weather conditions, different growing stages, and during the day before and after irrigating. The results show that the evapotranspiration of spring wheat is low or may be negative at night(20-08), but it increases from 08 o'clock in the morning and reaches the peak value about 16 o'clock, then decreases from 16 or 18 o'clock until minimum value about 02 to 04 o'clock at night. The evapotranspiration during clear day is higher than that during cloudy day, and the largest difference appears from 10 to 18 o'clock. After irrigating or raining the evapotranspiration of spring wheat increases to some extent. The relationships among evapotranspiration with air temperature and surface temperature are quadratic function curves at different times during a day.