Abstract: Combined with geology logging and well logging data, the petrological characters, pore types, sedimentary environment and diagenesis of clastic reservoir in Xishanyao Formation have been studied by SEM, casting thin sections, X-ray diffraction, and then the main controlling factors of this clastic reservoir have been analyzed, the high-quality reservoir distribution has been cleared, providing theoretical guide for further exploration and development.The results show that the Xishanyao Formation reservoir was developed in braided delta front, with underwater distributary channel facies as its main microfacies, being dominated by gray or celadon fine and medium sandstone, while its pore types contain residual intergranular pore, primary intergranular pore and intergranular solution pore, belonging to medium porosity and low permeability formation.The reservoir characteristics were destroyed by compaction and cementation during the diagenesis, reducing about 40%~70%and 5%~30% of primary pores, irrespectively; The secondary pores formed by the dissolution is constructive and take up 30% of the whole pores.Reservoir characteristics are mainly controlled by sedimentary environment compared to diagenesis; The high-quality reservoir is distributed in the underwater distributary channel microfacies of braided delta front.