Abstract: In the current technical specifications for trap evaluation, it is clear that reservoir conditions are one of the main factors for the probability evaluation of oil and gas. The key parameters and evaluation criteria need to be selected and established according to the characteristics of zones, fields and strata series. At present, they belong to qualitative evaluation. Structural and structural lithologic complex traps are mainly developed in the third subsection of the 4 th member of Leikoupo formation in western Sichuan region. In order to effectively evaluate the probability of oil and gas in the trap, the upper and lower reservoir sections of the third subsection of the 4 th member of Leikoupo formation are divided to analyze the correlation and difference of sedimentary microfacies type, reservoir lithology, physical properties and gas bearing properties. The results show that different favorable sedimentary microfacies are developed in the upper and lower reservoir sections of the third subsection, and the reservoir classification and fracture development directly affect the evaluation results of reservoir conditions, thus establishing the evaluation criteria of reservoir conditions. The practical application proves that the accuracy of probability evaluation of oil and gas in third subsection can be effectively improved by optimizing key evaluation parameters and semi quantitative evaluation of probability assignment.