The chamber-nozzle subsonic-transonic flowfield of solid rocket motor is computed by time-dependent method. The governing equations are numerically solved by MacCormack explicit scheme. The parameters of boundary points are calculated with physical boundary conditions and characteristic equations on the reference plane. It is shown that the numerical integral steps that have got to convergence for chamber-nozzle flowfield computation are much more than those for transonic nozzle flowfield calculation. Although the Mach number distribution along the wall and axis for chamber-nozzle flowfield is similar to that for transonic nozzle flowfield，the iso-Mach number line distribution doesn't agree with the transonic nozzle flowfield.