Abstract: For convenience of studying, various approximate formulas of PS-wave reflection coefficient derived from Zoeppritz equation are often used in AVO analysis and pre-stack inversion. These research results have not been systematically analyzed and summarized and so there exist some problems in practical application. Based on the detailed derivation of various approximate formulas, the assumptions, parameters, and applicability were summarized. Meanwhile, Ostrander and Goodway gas-bearing sandstone models were adopted to analyze the relative error of various approximate formulas with the change of incident angle. The results show that all the approximate formulas are suitable for small incident angle situation and the accuracy of formulas are closely linked with elastic parameters of up and down boundaries in big incident angle situation.