Abstract: On the basis of field measurement and core observation of Mesoproterozoic outcrops in Jibei depression and Xuanlong depression in Yanshan area, through integrated analysis on common thin sections, cast thin sections and SEM data, it is found that the reservoir rocks in the study area are mostly composed of dolomite, secondly of limestone and partially of siliceous rock, sandstone and breccia. The storage spaces of the reservoir are mainly composed of 2 storage systems that are micro?storage spaces in the matrix and macro?storage spaces of fissures and caves, in which the macro?storage spaces include 6 types such as tectonic fissures, interlayer fissures, dissolution fissures, dissolved caves (pores), constricted fissures and pressolution fissures, and the matrix pores are composed of intercrystalline pores, intergranular pores, alga?window pores, slightly dissolved pores (fissures), micro?tectonic fissures and micro?pressolution fissures. The sedimentary environment, lithology, diagenesis and tectonism are the main 4 factors influencing the storage spaces in the study area, among which tectonism and palaeo?karstification are the key factors to improve the storage conditions in the study area