Abstract: Two Chinese sorghum cultivars with different drought-resistant specialities are　tested to study the diurnal changes of photosynthesis rate and water use efficiency．The results show that the leave water potential，stomata1 resistance，photosynthesis rate and water use efficiency are higher in 3197B eultivar．And the transpiration rate in 3197B cuhivar is　lower than that in San-Chi-San cuhivar．This provides the background information for crop hreeding and cultivation in arid area．