Based on the core，logging，thin section and cathodoluminescence data，etc.，the main rock characteristics，lithofacies types，differential diagenesis characteristics and sequences of each lithofacies，multi-stage dolomitization characteristics and their genetic models in Mishrif Formation of X Oilfield are systematically sorted out，and then the control of each diagenesis on reservoir quality is analyzed. The results show that the bioclastic limestone in Mishrif Formation can be divided into 12 rock types and 5 lithofacies types according to bioclastic types and structural characteristics. It has undergone many diagenetic events such as the dissolution，cementation，dolomitization，compaction and pressure solution. The types and intensity of diagenesis of different lithofacies are compared and distinguished，and the mutual sequence and development characteristics of multi-stage atmospheric fresh water cementation，seawater cementation，formation water cementation and dolomitization are analyzed emphatically. Four kinds of dolomitization at the early，middle and late stages of bioclastic limestone are developed in the study area. Based on the analysis of the characteristics of dolomites in different lithofacies，it is concluded that the first type at the early stage is percolation-reflux dolomitization，the second is dorag dolomitization at the early stage，and burial dolomitization is at the middle and late stages. The genetic model of dorag dolomitization is discussed. In terms of controlling the difference in reservoir quality，the early cementation between bioclastic particles in some lithofacies is beneficial to the preservation of pores and the improvement of reservoir quality. The early dolomitization is generally beneficial to the improvement of local percolation，while the late dolomitization occupies the residual pores of the reservoir and reduces the quality of the reservoir.