Abstract: The relationships of water content to photosynthesis, respiration and water potential in three species of mosses, Plagiomnium acutum (Lindb.) T.Kop., Thuidium cymbifolium (Dozy & Molk.) Dozy & Molk., and Chrysocladiun retrorsum (Mitt.) Fleisch. were studied during May 20 to June 10, 1999. Among these three mosses, there are two types of water response models for net photosynthetic rate (Pn). One appeared in Thuidium cymbifolium and Chrysocladium retrorsum , in which Pn increased with the water content from 20% to 70%, but decreased from 80% to 95%. The optimum water content was 70%～80%. Another was presented in Plgiomnium acutum , in which net Pn increased with water content increasing from 20% to 80%, and a high level of Pn maintained from 80% to 95% of water content. The optimum water content was 80%～90%. In a wide range of water content from 60(70)% to 95%, the Rd remained relatively stable. But in the range of lower water contents from 20% to 70%, the Rd decreased with decreasing water contents.Changes in between water contents and water potentials within these three mosses are similar to each other. The whole curve of water contents to logarithm of water potentials appears to be S-formed.