In this paper, unsteady characteristics of pressure in solid rocket motor were analyzed by using response of pintle actuation, pressure and thrust data from ground test. Pressure and thrust in solid rocket motor can be controlled in real time by varying nozzle throat area with pintle, installed in the valve. Unsteady characteristics of pressure can be observed in this system occurred by various reasons.Two critical reasons, error of pintle actuation and ablation of center tube, are found and effects of each reason can be analyzed individually by re-prediction of pressure with response of pintle actuation and analyzing thrust to pressure ratio.