The total precipitable water in atmosphere is one of most important parameters in astronomical observation and meteorology．The measurement of total precipitable water in atmosphere by means of the Sky Brightness Monitor (SBM) is described. SBM is an exact tool used for precisely measuring various atmospheric parameters. The principles and method of measurement, the calibration method, and the performance of the water vapor measurement instrument are discussed, and the measurement results are given. The results indicate that the multi color photometric system of SBM can be used for the site survey in the western China for solar instruments.