The study on runoff variation characteristics and genesis is of great theoretical and practical significance for agricultural irrigation and water resource management. The Huaihe Basin (HRB) is an important agricultural area in China. Therefore,its characteristics and mechanism of runoff are very important. The runoff data from the nine hydrological stations in the middle and upper reaches of HRB are analyzed in its distribution,abrupt change characteristics and cycle variation,and the causes of runoff variation characteristics. It is found that the runoff of the middle and upper reaches of HRB accounts for about 70.37% of the total runoff from May to September,with the variation coefficient between 0.16 and 0.85,and the inter-annual extreme value ratio between 1.7 and 2.3. The runoff fluctuates in the middle reaches of HRB,and the trend of the runoff in the middle and upper reaches of HRB is decreasing,especially the runoff in April and May is significant and the seasonal variation is not obvious. The annual runoff of each site is significantly changed in 2000 s. The runoffs in stations Bantai,Wangjiaba,Lu Taizi stations have a small cycle of 2.0 - 3.4 years. The runoffs in the county,Huangchuan and Jiang Jiake stations were in the high energy area. The seasonality of flood in gand non-flooding periods are mainly in the 1980 s and the 1960 s. The response of the annual runoff to the climatic factors in Huangchuan Station is the most obvious,with significance of 95% and 99% for Multivariate ENSO Index and Pacific Decadal Oscillation (PDO) indices,respectively. The direct impact of PDO on the monthly runoff of each site was the most significant and mainly concentrated in June with a negative correlation. The results showed that the response of Southern Oscillation Index,North Atlantic Oscillation and the Nino3.4 sea surface temperature (Nino3.4) to the monthly runoff in the study area was significantly delayed,and Nino3.4 had a significant effect on the monthly diameter of the study area. The effect of the lag period is mainly in Huangchuan and Jiangjiaji,while the Arctic Oscillation and PDO indices have no lag response.