The study investigated spatial variability of spring wheat ET and uses regression analysis to identify the ET main factors. Furthermore, the ET main factors were taken into account in the ET space research. Results showed that the geo-spatial coefficients of variation of spring wheat ET ranged from 0.328 to 0.495 at various growing stages even for homogeneous farm fields. During the spring wheat growing season, the spatial variability of cumulative ET estimates was high at the tillering-shooting stage, and then reduced at the shooting-heading stage. Comparing to leaf area index (LAI), spring wheat ET had a significant relationship with surface soil moisture content change at all the growing stages. When the rainfall infiltration depth was less than 20cm, the soil moisture (0~20cm)was the ET main factor. Compared with the ground-based observations, the ET estimation precision with 42 ET ground sample data was better than 90%.