Abstract: The diurnal changes in the photosynthetic rate of an Aneurolepidium Chinens; community with environment Conditions were measured using an simulation chamber under field conditions. The diurnal change curve of photosynthetic rates in Aneurolepidium chinense community showed"double peaks"under normal conditions, one in the morning and another in the afternoon but it declined at noon. This behaviour can be correlated with environmental factors. Under good humidity conditions, the photosynthetic rate changed with photosynthetic active radiation; in drought condition, the photosynthetic rate was mainly effected by humidity. Using regression techniques, the relationship between photosynthetic rate and environmental conditions was y= - 4.28 +0.77x1-0.09x12 + 12.85x2 -8.71x22(where: y is photosynthetic rate, x1 is photosynthetic active radiation, x2 is relative humidity). The complex correlation coefficient of the equation was 0.92; relative error was 0.03 and the relative error of estimation was 0.21. Thus using the above model, the photosynthetic rate may be calculated and grass productivity predicted.