Abstract: This paper presents a discussion of the calculation approach to the pressure decay in the motor chamber and thrust transient,as a result of the blowing-out plug of reversal nozzles during the thrust termination process of the solid rocket motor. The delay time in the blowing-out process and correction to the exhaust coefficient Cw under the chamber pressure less than 2500 kPa is considered in the calculation of pressure decay. The transient thrust is calculated by use of the variation of thrust coefficient both in main nozzle and reversal nozzle with the chamber pressure. The tailoff impulse is calculated with integration. A comparison of theoretical calculation with testing results shows that the corrected theoretical calculation approach agrees well with the testing results.