For identifying the influences of soil moisture on transpiration rate, comparison between calculated and observed transpiration rates, responding to different soil moisture treatment, is carried out. The results show: (1) the calculation errors of transpiration rate in scarce water supply are higher than those in sufficient water supply; (2) the modified coefficients of transpiration rate are higher in scarce water supply than in sufficient water supply; (3) the calculation errors of transpiration rate decrease sharply after the modified coefficient taking into account. Meanwhile, the modified coefficient is statistically significant.