Based on the field experiment, the diurnal variation of the leaf water use efficiency of late rice under controlled irrigation was demonstrated, as well as the variation in the whole growing season. Relationships between leaf water use efficiency of rice and stomatal conductance and environmental factors including soil moisture and air temperature were analyzed. Difference of leaf water use efficiency between controlled irrigation and the check is not signiicant. Moderate soil moisture control can raise leaf water use efficiency. Within the whole growth season, leaf water use efficiency varied with soil moisture, much higher and lower soil moisture go against the elevation of leaf water use efficiency. With the increase of stomatal conductance, net photosynthesis rate, transpiration rate and leaf water use efficiency increased, but decreased when the stomatal conductance is too high. Influence factor analysis shows that leaf water use efficiency increased with the elevation of leaf-air temperature difference, carbon dioxide concentration and air humidity. To maintain high leaf water use efficiency, optimal scope of stomatal conductance, photosynthesis available radiation, air temperature and soil moisture are 200～350 μmol·m^-2·s^-1, 400～900 μmol·m^-2·s^-1, 28～34℃ and 85%～90% of saturated soil moisture, respectively.