Based on the data of monthly mean precipitation and water vapor pressure from 43 weather stations in Qinghai Province from 1971 to 2010, the precipitable water (PW) and precipitation conversion efficiency are calculated by using an empirical formula of atmospheric total PW for the four ecological function regions, i.e., the eastern agricultural area, area of Three Rivers Sources, the area around Qinghai Lake and Qaidam Basin. The results show that the precipitable water of all ecological function regions presented a unimodal distribution form, with the maximum in the summer. The precipitation conversion efficiency over the area of Three Rivers Sources and the eastern agricultural area presented a bimodal distribution, but a unimodal distribution over Qaidam Basin and the area around Qinghai Lake. The precipitable water of all ecological function regions had increased during the 40 years, especially in Qaidam Basin and the area around Qinghai Lake. There were abrupt changes of PW in all ecological function regions; in the eastern agricultural area and Qaidam Basin abrupt change happened in 1983 and 1996, respectively; in the area of Three Rivers Sources and the area around Qinghai Lake abrupt change occurred in 1993. The PW had increased gradually from west to east, and the precipitation conversion efficiency had decreased towards Qinghai Lake.