Abstract: It is an important gasbearing strata in T3x2 reservoir in the Xujiahe Formation of Upper Triassic，Sichuan Basin.But the inhomogeneity of the sand bodies is serious，and low porosity and permeability of the reservoir directly influence the exploration and development effect of the oil and gas well.This paper is aimed at proposing the conception of synthetical diagenetic facies，the purpose of which is to find out an effective method of forecasting the range of profitability of the reservoir.Synthetical diagenetic facies is just a complex which takes the dominant part in the multidiagenesis folded and reformed under different diagenetic environment.Compared with unifactor diagenetic facies，synthetical diagenetic facies can reflect the diagenetic characteristic of the reservoir better，which has the analysis of the main diagenesis，also has the analysis of the strong and weak order of the main diagenesis.According to the optical thin section study，core observation and the research of unifactor diagenetic facies，the paper divides the diagenetic facies in T3x2 Segment reservoir into 7 types，and researches the synthetical diagenetic facies in the T3x2 Section reservoir in Sichuan Basin.The research result indicates that the developmental condition of the T3x2 reservoir is centralized relatively，and the reservoir develops well in the middle of the basin，and develops badly in the edge and the east area of Sichuan Basin.Therefore，the part of the middle and the west area of Sichuan Basin is the range of profitability in the exploration and development in T3x2 Section reservoir.

Key words: Sichuan Basin, T3x2 reservoir, tight sandstone reservoir, diagenesis type, diagenetic facies 