Based on the analysis of working process of ejection gun of rocket ejection seat,the physical and mathematical models of interior ballistics of ejection gun were established and the interior ballistics parameters of a rocket eject seat were validated by test and calculation. The measured chamber pressure curve is consistent with the calculation curve. The calculation value and measurement value of the maximum pressure p_m, working time t_g, nuzzle pressure p_g and nuzzle velocity v_g are 24.20(24.57) MPa, 157(155)×10^-3 s, 22.27(21.83) MPa, 16.61(16.59) m·s^-1, respectively. And the largest error of their characteristic parameters is less than 3%.