Abstract: The commercial gas has the same seismic response as the fizz water or fizz gas,which all show the high amplitude response.The amplitude attributes or common elastic parameters cannot identify the commercial gas reservoir.Considering the high sensitivity to gas saturation,density can be used to indicate the commercial gas reservoir.In the Bayesian inversion framework,the prestack inversion based on Trivariate Cauchy distribution can reduce the influence correlation between the P-,S-wave velocity and density parameters,which can improve the inversion reliability.Model test verifies the high accuracy of the inverted density parameter.The technique has achieved good application effect in M Block.Under the guidance of fluid substitution and rock physics analysis,the density parameters were extracted by prestack seismic inversion based on Trivariate Cauchy distribution,and the commercial gas reservoir was predicted,which was confirmed by the drilling well.The application in M block showed the high practicability of this method.