The paper is based on long series hydrologic data and the percentage of forest cover change data about Chuxiong hydrometric station and Xiaohuangguayuan hydrometric station of Longchuanjiang gorge. Wavelet analysis and statistical analysis are used to study on the interrelation among precipitation、vegetation and runoff variation, and they are also used to study the essence and generation system about quasi periodic change of different timescale runoff volume. The result indicate that the study region's precipitation series exists 2 a、4 a and 14.5 a quasi-prime period, runoff volume series exists 2 a、4 a、6 a and 22 a quasi-prime period, among them, runoff volume's low frequency oscillation reflects the quasi periodic variation about the runoff comes from soil and the groundwater runoff exists in rifts, high frequency oscillation reflects the quasi periodic variation about the surface runoff. Seasonal variation and annual high frequency oscillation of runoff are mainly caused by precipitation change. Runoff series' quasi-prime period around 6 a and 22 a is owing to the forming of soil and rifts' magnifing the precipitation series 4 a and 14.5 a prime period, runoff series' 4 years quasi period is formed by the special physical geographical environment. There is a sudden change of relationship between runoff and precipitation in 1969.
