Abstract: By using the data from 150 meteorological stations in Sichuan and the NCEP reanalysis data, and the methods of correlation, wavelet and synthetic analysis, a new plateau monsoon index (Div_PMI₂) was constructed by improving the Div_PMI. The possible reasons for the abnormal spring drought caused by the plateau winter monsoon were analyzed. The results showed that in most areas of Sichuan Province, the number of spring drought days tended to decrease weakly, but the spring drought-prone areas (western and southern Sichuan Basin and mountainous areas in southwestern Sichuan) tended to increase significantly. The Div_PMI₂ was always positive (negative) in winter (summer) from 1961 to 2016. Therefore, the new index can better characterize the transition time and relative strength of the plateau monsoon compared to several typical plateau monsoon indices. The Div_PMI₂ index has higher correlation and more similar periodic oscillation characteristics with the average spring drought days than other indices in Sichuan province. The analyses of circulation showed that the Siberian high was weakened and the height field in the bay of Bengal and the plateau was positive anomaly when the plateau winter monsoon was strong. As a result, the cold air in the north was weak, the development of low-value system in plateau was hindered, and the southwest warm and humid air flow could not be transported to Sichuan. In addition, the middle troposphere was controlled by subsidence airflow, and water vapor diverged outward, which led to sunny and rainless weather and spring drought in this area.