Using annual nature runoff data from 1961–2000 for the Qinghai—Tibet plateau Nyangqu River, the Mann—Kendall method and wavelet transform were adopted to analyse runoff variation characteristics for the Nyangqu River. The results show that the annual change in runoff is relatively stable and that the intra—annual distribution of the runoff is extremely uneven. The disparity in runoff between wet seasons was significant. The runoff for June–September accounted for 65% of the whole year and the highest monthly runoff accounted for 24.56%. From 1961–2000, runoff showed a significant increasing trend with an abrupt increase in 1985. The 5–8 years oscillation period of the runoff was most notable and the 10–15 years period was relatively notable. The principal periods of annual runoff for Shigatse station and Gyantse station were 5a and 7a. The second were 13a and 12 years. Increasing glacial melt water caused by rising temperatures may be the main reason for increased runoff in the Nyangqu River.