Based on the observation of microscope and the measurement of homogenization temperature of fluid inclusions, the characteristics of fluid inclusions and the accumulation period of Miocene reservoir in Ledong-Lingshui Sag of Qiongdongnan Basin are discussed.The results indicate that the fluid inclusions are mainly distributed along the healing fissures in quartz,partly distributed in the side of quartz granules or through multiple clastic particles. The types of fluid inclusions mainly include brine inclusions, liquid hydrocarbon inclusions, gaseous hydrocarbon inclusions and gas-liquid hydrocarbon inclusions.The hydrocarbon inclusions are developed in three phases, which present yellow and blue-white fluorescence with high organic maturity. The distribution of homogenization temperatures is discontinuous and concentrates in the range of 130℃ to 150℃. According to the comprehensive analysis of characteristics and occurrence of fluid inclusions, and homogenization temperatures, it is determined that the Miocene reservoir experienced three phases of hydrocarbon filling and one phase of CO2filling, which happened in the late stage of natural gas injection, and the second and third phase of hydrocarbon filling are the main period of hydrocarbon accumulation. Combined with the burial history and thermal evolution, it can be concluded that the main period of hydrocarbon accumulation is 1.9Ma~1Ma.