T-R sequence framework of Meishan Formation in Ledong Sag，Qiongdongnan Basin was established and its evolution process of submarine fan deposits was discussed in detail according to the comprehensive analysis of 3D seismic and drilling data，combined with the rising and falling characteristics of regional sea level. Results reveal that five large-scale transgression-regressive cycle events happened in the study area during the middle Miocene，and the source of main clastic materials in Ledong Sag migrated from Hainan Uplift in the early stage to Vietnam in the late stage. During this process，three stages of large submarine fan deposits with different distribution directions and scales were formed in Ledong Sag.Combined with the controlling factors of regional oil and gas accumulation，it is believed that the submarine fan sandstone of Meishan Formation was cut by the central Canyon of Huangliu Formation in the late period；the composite lithologic traps of Meishan Formation submarine fan-Huangliu Formation channel sandstone were formed under the overall mud-sand sedimentary background，which communicated with deep source rocks of Yancheng Formation through diapirs and fractures，forming“lower generation and upper reservoir”type lithologic reservoirs.Under the guidance of this understanding，the composite lithologic traps of Meishan Formation submarine fan-Huangliu Formation channel sandstone have been successfully drilled，with proved natural gas reserves of nearly 100×108 m3.