The atmospheric PWV (precipitable water vapor) was derived from GPS observations of 5 stations over Hong Kong during four years from 2013 to 2016 and the accuracy of PWV(GPS) was assessed with PWV(ECMWF). Based on harmonic analysis, the PWV(GPS) was then compared with rainfall. Taking PWV(ECMWF) monthly means as reference, results show that the RMS(root mean square) of PWV(GPS) monthly means is between 1.02 mm and 3.07 mm and the bias is between -2.14 mm and 2.52 mm. Both PWV and rainfall have similar periodic characteristics. The peaks of PWV occur in July with amplitudes varying between 14.65mm and 16.79mm. And the peaks of rainfall also occur in July and the amplitudes are between 147.64 mm and 211.01 mm. The annual increase rate of PWV is positive at each GPS station, which indicates that the PWV over Hong Kong has an increasing trend during the past 4 years. While the annual increase rate of the actual rainfall is negative except in HKOH station, which means a decreasing trend during the 4 years.