Based on introducing the main quantitative indexes ofcorrelation dimension D2 and Kolmogorov entropy in rebuilding time series imbedding space, the relationship between built-in dimension m and correlation dimension D2 is discussed with the precipitation time serial in Sichuan middle region of Yangtze River upstream. The saturation correlation dimension, minimum built-in dimension and Kolmogorov entropy are calculated and given, that is D2=5.11,m=10 and k=0.338. Primary component analysis method is applied to validate its chaotic character, and obtained that the forecasting length for this precipitation time serial would not exceed 2.96 year. This time serial chaotic analysis will provide a scientific gist for precipitation forecasting.