After analyzing the daily precipitation and sunshine duration data from September to October of 1960-2011 from 601 stations in China, a new autumn rain index was proposed by comparing it with the autumn rain indices presented by others, and combining the weather and climatological characteristics of autumn rain in western China. We also examined the proposed index by using high-resolution empirical orthogonal function (EOF) analysis. The results suggest that the modified autumn rain index better describes the geographical distribution and variations in autumn rain intensity, as well the interannual and interdecadal characteristics of autumn rain in western China. The application of the new index also suggests that autumn rain is consistent throughout western China. According to the power spectrum, the autumn rain index exhibits a quasi 6-year oscillation on the interannual timescale and pronounced interdecadal variations. In western China, the autumn rainfall was above normal during the 1960s to early 1970s and 1980s to early 1990s, whereas there was less rainfall in the mid to late 1970s, the late 1990s, and in the early 21st century. However, the autumn rainfall in western China has been increasing since the mid 2000s.