Traditional method for retrieving precipitable water vapor was evaluated with the data obtained from series of long time in-situ measurements of CE-318. The results show that the method has a low accuracy and is not suitable for applications over this region. In this paper, the theory of precipitable water vapor detection with NIR channels was introduced. Equations of precipitable water vapor remote sensing were derived and analyzed. Retrieving method for FY-3A/MERSI（Medium Resolution Spectral Imager）was proposed. Comparing with the results of CE-318 in-situ measurements in the studied area, it was concluded that precision of the method relied so much on reflectance of the underlying surface. The method of three-channel ratio had better performance than that of two-channel ratio by reducing the errors from 16.1% to 14.3%.