Abstract: This paper examines the influence of the Madden-Julian Oscillation (MJO) on the characteristics of persistent heavy rainfall (PHR) over Hainan Island for the period of 1979-2019. It is unique that abundant PHR amounts and significant rainfall variability are observed on Hainan Island during October, which are tightly connected with the stronger MJO events. The results show that Hainan Island has more PHR when MJO is in phase 3-6 (i.e., the active convections over the tropical East Indian Ocean-Western Pacific), and less PHR when MJO is in phase 7, 8, 1, and 2 (i.e., the active convections over the tropical West Indian Ocean and the central Pacific). The active MJO convections in phase 3-6 cause the MJO disturbance easterly over Hainan Island, with northeast wind anomalies from the north and a cyclone circulation anomaly over the north-central South China Sea. It is consistent with the typical circulation mode of the autumnal rainstorm on Hainan Island, which enhances the low-frequency water vapor flux convergence and humidifies the lower atmosphere, resulting in more PHR on Hainan Island. The MJO disturbance anticyclonic circulation over Hainan Island could limit convergence of water vapor flux and lower atmospheric moistening, when the MJO active convections are in phase 7, 8, 1, and 2. The warmer SST in the tropical Eastern Indian Ocean-western Pacific and the lower SST in the tropical Eastern Pacific contribute to the local MJO convections in phase 3-6, which could strengthen PHR on Hainan Island.