By using FACE system, the microclimate in rice canopy and related physiological indices were observed continuously from the elongation to the maturing stage of rice growth, and the effects of FACE on the rice canopy evapotranspiration and water use efficiency were studied and simulated with energy balance analysis. The results showed that using P-M equation to describe the quantitative relationships of rice leaf stomatal conductance with photosynthetically active radiation (PAR) and vapour pressure deficit (VPD) could better simulate rice canopy evapotranspiraton under FACE and ambient conditions. During observation period, the total water use of rice in FACE plot had a 10 mm decrease, compared with that in control plot. Considering of the 12% increase of total biomass, the water use efficiency of rice under FACE condition was increased by 12%.