The hydrologic variability of the international river and its transboundary influences have become a worldwide concern. Analyzing the variation characteristics of runoff and its impacting factors could provide the basis for the reasonable utilization and management of transboundary water resources. Based on the discharge data of 6 hydrological stations and temperature and precipitation data at 64 meteorological stations in the Red River Basin, we analyzed multi-temporal scale changes of runoff, and the influences of climate change and human activities on runoff were discussed. We found that the intra- annual distribution of runoff was uneven and 80% of runoff was concentrated in the wet season (June to November). Intra-annual distribution of runoff for tributaries was more uneven than in the main stream. Furthermore, the concentration period of runoff at all stations showed an advance trend. Especially,Manhao,Yen Bai and Ghen Ga station had advanced trends. Inter-annual variation was acute, with significant differences between wet and dry years. This shows that low water periods appeared from the mid-1950s to mid-1960s, high water period from the mid-1960s to mid-1970s, flat partial dry period from mid- 1970s to mid- 1990s, flat partial wet period from mid- 1970s to 2002, and low water period after 2002. Mean annual runoff decreased in the past 50 years. Lixianjiang station showed a significantly decreasing trend. According to the results of R/S analysis, annual runoff will increase in the future. Wavelet analysis showed that annual runoff at Manhao and Lixianjiang stations had change periodicities of 4a,6~9a and 21~22a. Similarly,Son Tay station had a change periodicity of 8~10a and 21~22a. Significant change periodicities of 21~22a were found at the three stations. The most important factor causing decline of discharge in the Red River was precipitation. Human activity was also an important factor which influenced the intra- annual distribution of runoff;however, the impact of human activity on runoff was limited at an annual scale.