Abstract: Tight reservoirs can produce considerable oil and gas, which is closely related to the development of micro-fractures in the formation. Therefore, it is very important to evaluate the degree of fracture development in tight reservoirs and determine the fluid properties. The forward simulation of pore and fracture theory shows that the velocity of longitudinal and transverse wave is sensitive to fracture parameters and fluid properties. Based on this, the inversion objective function is constructed by using the P-and S-wave velocities calculated by the theoretical model and the measured P-and S-wave velocities, and the fracture density and fluid modulus are obtained by inversion. The application shows that the inversion results are consistent with the test results, and the application results are remarkable.