This research had collected the maximum daily runoff and daily rainfall data of Chu-Cow watershed, Chang-Pan watershed, and Gin-Haw watershed, which are located in Pa-Chang River basin, from 1995 to 2004. It also explained the ways of reasoning the time of concentration and runoff coefficient in different watersheds. This research makes use of Geographic Information Systems to analyze the effects of the degree of development and slope of each watershed. The relationships between different watershed’s slope, time of concentration and rainfall intensities were also discussed. This preliminary research inquired into the statistical characteristics from the actual measurements in the historical flood, and summed up the influences of the geographically characteristics of Pa-Chang River watershed. The results of this research showed, except for that Chu-Cow watershed, that the correlation between surface runoff and river discharge are moderate. In analyses of the effects on slope, we have found that during typhoon and torrential rain, the slope of watershed did affect the time of concentration and runoff coefficient, because of the higher urbanization of Pa-Chang River, including the increase of population, and changes of land exploitation. Among the urbanized district, the various floods of medium and small rivers gather rapidly, and they often cause serious flooding in the downstream area. This research suggests that the use of Geographic Information Systems to investigate the watershed environment is essential in the future. Owing to the relationship between nature environment and land exploitation are complicated, it could have great differences according to the various characteristics for different districts.