Abstract: The diagenesis, reservoir space and controlling factors of Mesozoic clastic reservoirs in Zhuanghai area have been researched in this paper through core observation, thin section determination, scanning electron microscope and X-diffraction analysis. The results show that, the clastic reservoirs experienced strong compaction, cementation and metasomatism as well as polyphase dissolution and crack formation. The diagenetic processes can be divided into four stages including early diagenesis B,middle diagenesis A1 and A2 and middle diagenesis B. There exist two chief types of reservoir space: the one is fractures including structural fractures, compaction fractures and cleavage cracks; the other is secondary pores including feldspar dissolution pores and carbonate cement pores which are related to atmospheric water dissolution and organic acid dissolution during the course of organic matter evolution in Shahejie Formation and Dongying Formation. The Mesozoic clastic reservoirs in Zhuanghai area are chiefly affected by sedimentation, diagenesis and tectonism. Sedimentation controlled the textures of clastic rocks such as matrix,sorting and rounding, and further affected the texture of primary pores, which served as basement for later dissolution. As the migration pathways of fluids, the faults and unconformity surfaces supplied acidic media for dissolution. Therefore, the scale of faults and unconformity surfaces controlled the properties of clastic reservoirs obviously. The closer the distance from faults and unconformities is, the better the reservoir properties are. In the areas of favourable sedimentation and geotectonic conditions with good primary pore structure, weak compaction and cementation, and well developed fractures, the strong dissolution, good primary pores and reservoir properties were formed, leading to development of several secondary pore zones around the unconformity surfaces, and the most favorable secondary pores occurred on the top of Mesozoic during the middle diagenetic stage A1.