Based on the measurements of eddy covariance (EC), the water vapor flux of Phyllostachys edulis forest ecosystem was analyzed from January to December of 2011 in Anji County, Zhejiang Province of the subtropical China. The annual changes of water vapor flux and its budget, also include the responses to precipitation, net radiation (Rn) and vapor pressure deficit (VPD) were investigated through to combined with conventional meteorological data. The results showed that annual water vapor flux was positive value, which discovered that moso bamboo forest was the source of water vapor, as well as the water vapor flux had distinct diurnal and seasonal variations. On a monthly curve, the diurnal changes of water vapor flux were in a single-peak type, the maximum values were all at 12:00-14:00, showing a regularity pattern, the maximum presented in July (0.1116 g m^-2 s^-1),the minimum (0.0209 g m^-2 s^-1) in December. On a seasonal scale, the water vapor flux presented a single peak typically in Summer, and the maximum value was 0.0873 g m^-2 s^-1, the variations of Spring and Autumn were similar to Summer, both of them were 0.0541 g m^-2 s^-1. However, in Winter it varied much more intricately, fluctuating greatly, which showed that there were some smaller peaks except a high peak. Besides, the annual evapotranspiration of the forest was 744.72 mm, slightly lower than that of other types of woodland Korean Pine forest and Cunninghamia lanceolata forest. The annual evapotranspiration of the moso bamboo forest was about 48.26% of the annual precipitation, which is 1543.10 mm. Except February, April, May, November and December, evapotranspirations of all the other months were less than precipitations. In June, the differences between evapotranspiration and precipitation appeared obviously significant.Rnwas the main driving force of evapotranspiration and was a key factor on the energy balance. Through this study of regression relationship between water vapor flux and different net radiation analysis, there were a high correlation between them. And the squares of correlation coefficients ( R 2) were 0.2605 in Spring, 0.6111 in Summer, 0.5295 in Autumn and 0.0455 in Winter. Therefore, this result showed that there existed significant linear relationship between water vapor flux and net radiation at different temporal scales by F test. In addition, using the data of VPD of the moso bamboo forest from June to September, the height of which was 1m from the ground to the canopy, and the result suggested that before moso bamboo vegetation matured, water vapor flux was strongly linearly increased with the increasing of VPD. But the evapotranspiration was depressed after its matured, as the increasing of VPD when it surpassed certain extent. The research suggested that the quadratic equation fitting of correlation coefficient (R² from June to September, 0.4251, 0.2955, 0.3806 and 0.2312) was much higher than the exponential fitting's.while the R² were 0.3708, 0.2021, 0.2666 and 0.2137, and it also displayed that there was significant linear relationship between water vapor flux and VPD by F test during the time series.