Addressing the issue of jamming caused by excessive deformation of the casing after actuation in sealed pyrotechnic actuators, a reliability design method for the casing wall thickness based on the stress-strength interference model is proposed. And a detailed calculation example for a typical sealed pyrotechnic actuator is provided. Using a validated simulation model, the functional relationship between the casing deformation after actuation and the casing wall thickness is calculated and fitted. The first-order second-moment method is employed for iterative computation to determine the design point for the mean wall thickness that corresponds to a given standard deviation and meets the reliability requirements. The results show that when the standard deviation of the casing wall thickness is 0.1 mm, the design point for the mean wall thickness is 1.34 mm. At this point, the reliability that the casing deformation after actuation does not exceed the clearance size between the casing and the mounting hole is 0.990 9, and the casing mass is reduced by approximately 7.7% compared to that designed by the conventional safely factor method. This method allows for adjustments by controlling both the mean and standard deviation of the casing wall thickness, offering significant technical and economic benefits.