The bilateral reliability model for initiating explosive devices was studied in order to improve the assessment precision. The calculation method was proposed for the lower limit of bilateral reliability based on the classical two-rank approximate limit,and the simulation tests were conducted By Monte Carlo method. Results show that the precision is suitable for the requirements of reliability assessment for initiating devices when the amounts of samples are 20-30. And the feasibility and applicability is validated by tests with stab detonators compared with the other methods.