Abstract: Through reviewing the research achievement of crop evapotranspiration at present, the research status of different spatial-temporal scale models and scale conversion methods of crop evapotranspiration was described, and the development trend of research on crop evapotranspiration was hereby forecasted. First, based on remote sensing data, digital elevation model and GIS technology, new spatial interpolation method was established to realize the spatial scale conversion of crop evapotranspiration from the precise point scale to the large scale. Then, on the basis of remote sensing data, accurate crop coefficient model was built to realize temporal scale expansion of crop evapotranspiration by a temporal scale expansion method based on crop coefficient. Finally, a comprehensive and operational model of crop evapotranspiration was established through the spatial-temporal scale conversion method.