Based on fandamental equations for two-phase f1ow in combustion chambers of solid propellant rocket motors，this paper derives calculation equations taking into accoant erosive burning and two-phase f1ow. A numerical solution to these equations is discussed in detail; the effect of variabi1ity of cross-sectional area of channel along the 1ength， which is caused by erosive burning，and two-phase f1ow on pressure-time curves and f1ow field in chambers is analysed. It is useful for predicting pressure-time curves accurately and calculating f1ow field in chambers thoretically.