The present study took the Napahai ungauged subalpine wetlands as an example and built an empirical correlation model between the climatic factor and the hydrological factor based on the time lag effect of basin runoff. This model took advantages of the climatic factor to simulate the fluctuation of hydrological factor. Forty-eight scenes of Landsat Thematic Mapper/Enhanced Thematic Mapper Plus(TM/ETM+) images from 1990 to 2011 were catalogued to extract the open water areas(OWA) in the wetlands. Then the accumulated daily precipitation(ADP) levels at different time steps were generated by statistically computing the daily rainfall data in the study area. Through regression analysis between OWA and ADP at different time steps, optimal accumulated daily precipitation(OADP) was screened out and the empirical correlation model of OADP-OWA was also obtained. And then with the help of empirical equation between open water storage(OWS)- OWA in Napahai wetlands, the correlation model of OWS- OADP was established. The simulated results showed that the hydro-regime of Napahai kept stable in the dry season(November to April) and fluctuated sharply in the rainy season(May to October) on the inter- annual time scale. On the intra-annual time scale, the average monthly OWS raised in July, got maximum of 8.66*10~6 m~3 in September, then rapidly declined in October, and kept stable of 0.95*10~6 m~3 from November to July in the next year. September was the most urgent month for protecting the surrounding villages from flooding. This is basically consistent with the data from field surveys and remote sensing image interpretation information. It is suggested that the above model could simulate the fluctuation trends of the OWS in Napahai wetlands and could effectively reduce the influence of data deficiency on the quantitative simulation of hydrological regime in wetlands. The above model provides a new vision for hydrological studies of ungauged subalpine wetlands, and offers the basic data and method for preventing the flood in this area.