The reservoir in Huaqing area is characterized by poor properties and large diferences of properties between adjacent wells．This paper analyzed the major factors of resulting in diferences of reservoir properties from the two aspects of sedimentation and diagenesis．By using core observation，cast thin section and scanning electron microscope，this paper studied the sedimentation and diagenesis of Chang 8 reservoir in Huaqing area．The result shows that multi-source of deposition is an important cause of obvious differences of Chang 8 reservoir properties in Huaqing area,the sedimentary quality from the northeast is better than that flr0m the southwest in respect for sorting coeficient and average pore size．and the effect of diagenesis on reservoir properties is different．Based on the effect of diagenesis on reservoir properties，three combinations of diagenesis are divided as follows：dissolution and chlorite rim cementation is the best combination with relatively high porosity and permeability，the combination of strong compaction and carbonate cementation severely damaged the reservoir properties，and the effect ofthe combination ofkaolinite or illite cementation and dissolution is moderate．