Based on a certain type of solid rocket motor, in this article, the structure of nozzle insert was optimized by six sigma statistics a-nalysis method and design of experiment method. Through lots of comparative studies and imitation analysis, the angle between the axial contact surface and the nozzle wall was chosen as the main factor of the stress distribution in the nozzle insert. Meanwhile, simulation ex-periment proved that the angle affects the stress of nozzle insert obviously. Research shows that the nozzle inserts will be in the best favora-ble stress state as while the angle reaches 90 degrees, and the maximum stress value is reduced from 77.54 MPa to 48.41 MPa to ensure the nozzle insert maintains structure integrity and satisfies the requirements of the certain type of solid rocket motor.