Using methods such as the non-parametric Mann-Kendall test, linear trend analysis, and wavelet variance analysis, the precipitation and runoff in the Western Sichuan Plateau reach of the Dadu River Basin from 1991 to 2020 were analyzed. The results indicate that over the past 30 years, the annual precipitation in the region showed an overall upward trend, with a variation rate of 29.7 mm/10a. The year 1997 was an abrupt change year with the dominant cycle of approximately 8 years. Precipitation in different seasons generally exhibited increasing trends, albeit with differing abrupt change years and certain periodicities. The average streamflow across the annual, flood season, and dry period series all demonstrated a steady upward trend, with alternating wet, normal, and dry years. The coefficient of variation (CV) was lower in the downstream area compared to the upstream. The year 1992 was a significant abrupt change point for a notable increase in runoff. Furthermore, the peaks and troughs of the runoff hydrographs corresponded well between the upstream and downstream sections, with the timing of maximum and minimum runoff occurrences being synchronous.