To assess the high reliability of initiating explosive device with small samples, the test design plan with small samples for initiating explosive devices was studied. Based on test information entropy, a new test design method was put forward. With this method, reliability of No.54 stab detonator which is used in head kindling organ of H/DR131 fuze was assessed. Twenty-two products were tested on the stress level of 4.5 cm and all fire. The assessment result is in agreement with the test result with 1800 samples. The product meets the reliability requirements with reliability of 0.999 at the confidence level of 0.90.