Estimation of evapotranspiration （ET） is an obstacle in researches of both water and energy balance. In this paper

three-temperature （3T） model was revised for remote sensing application. A case study was performed in a semi-arid grassland from July to October in 2008 in Taibus Banner of Inner Mongolia

China. Eleven cloudless MODIS images at 1 km scale were used to estimate ET and data observed from two Bowen ratio systems in the corresponding period was adopted to validate the performance of the 3T model. Results showed that: （1） the modeled ET varied from 1.28 mm/d to 9.03 mm/d in the growing season

with a mean value of 4.58 mm/d; （2） the modeled daily ET distributed homogeneously in space

and temporally

ET value increased and then decreased gradually as the growing season changed from beginning to the end; （3） the mean absolute error between the observed and modeled ET was 0.58 mm/d

with maximum and minimum absolute errors of 1.64 mm/d and 0.11 mm/d

respectively

and the mean absolute percent error was 17.10%. All the performances indicated that the 3T model has a good potential in ET estimation.