Abstract: The changes in hydrology of the Suomo River resulting from climate fluctuation and land cover changes during 1960-1990 were analyzed. During this period, Suomo basin experienced increases in annual precipitation, streamflow and floods . Annual precipitation increased with a rate of 0.45-1.71mm/a, while heavy rain events did not show significant upward trends.In the dry season temperature increased , in raining season temperature decreased. While annual mean temperature changed little .During 1957-1974, forest coverage decreased and droped to 25% in 1974. After that, it began to rise and reached 30% in 1985. The storage of forest decreased from 423m³/ha in 1957 to 177m³/ha in 1998. In the meantime, the hydrologjcal system changed obviously. Annual streamflow became increasingly great and upward trend was more significant than that of annual precipitation. In the 1970's,annual runoff increased by 6.5% than that in the 1960's. In the 1980's annual runoff increased by 15% than that in the 1960's. In the 1970's and the 1980's, precipitation was 19.4mm and 39.9mm more than that in the 1960's.While runoff increased 37.7mm in the 1970's and 87.0mm in the 1980's. According to water balance equation, evapotranspiration decreased by 10% in the 1970's and 25% in the 1980's respectively. The annual potential evaporation is 900mm in the basin,while real evapotranspiration is only about 200mm based on water balance for many years.Thus,decrease in evapotranspiration resulting from temperature change is small,the main reason for evapotranspiration decreas is that rainfall interception and soil water storage decease which is related with land cover change in the basin. Flood events became more often and serious during 1959-1999. Soil erosion increased greatly and its upward trend was most significant.