Abstract: The Jiyuan Sag is a Mesozoic-Cenozoic superimposed basin, formed on the basis of the Paleozoic platform of North China by complex tectonic movement. The sag is characterized by complicated hydrocarbon accumulation systems, after multi-stages of charging, destruction and transformation of hydrocarbons. So far the Mesozoic hydrocarbon accumulation phases in the sag have still remained unclear. Fluid reservoir inclusions, as an effective tool, may provide various information related to hydrocarbon accumulation, such as temperature, pressure, fluid composition and paleoenvironmental characteristics, etc., and are commonly used for definition of thermal evolution stages of source rocks and division of hydrocarbon generation and charging stages, the restoration of fluid paleopressure, as well as the analysis of hydrocarbon accumulation process. In this paper, fluid inclusions are used to study the hydrocarbon accumulation phases for the thermal evolution of the two set of major source rocks, the Lower Jurassic Anyao Formation and the Upper Triassic Tanzhuang Formation, in the sag.Systematic analysis method and the indirect projection dating method for homogenization temperature-burial history were used to analyze the characteristics of fluid inclusions for dividing the hydrocarbon accumulation phases.The results suggest that there are 7 kinds of hydrocarbon inclusions in the Mesozoic reservoirs of the Jiyuan Sag, including oil inclusions with three kinds of fluorescence colors in blue-green, yellow-green and blue respectively, and pure gas-phase inclusions; According to the fluorescence color and homogenization temperature of inclusions, host mineral occurrence and its diagenetic sequence in addition to other characteristics, it is considered that at least 3 phases of oil charging (163 Ma, 101~95 Ma and 27~23.8 Ma) and 1-period of gas charging (119~115 Ma) have occurred in the sag.