Abstract: A computational model with an implicit numerical integration scheme is successfully applied to computation of the one-dimensional time-dependent two-phase transonic flow field in nozzleless solid propelland rocket motors.In addition,this achievement provides the basis of integrative performance calculation for all kinds of solid rocket motors.We introduce a concept of equivalent ignition channel,which simplified the treatment of headstream boundary conditions.When deducing the expressions of the elements in the coefficient matrix,we get derivatives before we replace the differential with finite difference.This approach not only makes the expressions succinct,but also saves the time of computation.In the inverse operation of the matrix in two-phase flow computation,the characteristics of the matrix are taken into account,and therefore the computation time is further shortened.Two numerical examples are given.Comparison of the calculations with the motor tests shows a good agreement between the calculated and the measured values.