Formation mass density is directly related to porosity, fluid type, fluid saturation, and matrix mineral composition. The change of the reservoir parameters can cause the change of density and then the seismic velocity, impedance and amplitude. We discussed the characteristics of the changes by theoretical calculation and presented a method for estimating density and porosity based on full acoustic waveform inversion. Because of avoiding the signal distortion caused by more processing, the method can improve the inversion accuracy of density and porosity. It also can eliminate noise by integrating the derivative of wave field along time and summing multi-shot data. The method has been tested successfully by a synthetic example and gas-field data from western China. The density and porosity provided by the method agree with the logging result. It also supplies reliable data for prediction of effective reservoir and calculation of reserves.