The preprocessing of well log data and shear wave calculation are the precondition and base of prestack inversion.We study the Jurassic San Gong He group reservoir bed by simultaneous pre-stack & post stack inversion in XiaYan 15 borefild,the results of test demonstrate that the velocity ratio of compress to shear wave is more sensitive than acoustic impedance on identifying the lithologic character and fluid property.It approve that pre-stack inversion is an effective method on identifying the complex reservoir bed and hydrocarbon bearing interval.