To explore the water use efficiency of Rosa xanthina L. in Loess Hilly region, the light response process of photosynthetic parameters of R. xanthina was measured under eight soil moisture conditions with CIRAS-2 portable photosynthesis system to elucidate the quantitative relationship between water use efficiency of R. xanthina, soil moisture and light intensity. The results show that: 1) The photosynthetic rate (P_n ) of R. xanthina has a certain response to the change of relative water content (R_WC); The photosynthetic rate keeps at a high level when R_WC ranges from 44.5% -66.5% and peaks when R_WC is 66.5%. 2) R. xanthina leaf transpiration rate (T_r) is sensitive to R_WC changes, reaching the highest level when R_WC is 66.5%, and will significantly reduce as R_WC increases or decreases. 3) The water use efficiency of R. xanthina is at a high level when R_WC changes from 22.9% -54.5% and culminates when R_WC is 44.5%. The water use efficiency of R. xanthina is insensitive to light intensity, keeping always at high levels when the light intensity varies from 800 -2 000 μmol/ (m²·s).