In order to improve the function reliability of explosive null gate, the traditional and weak gap explosive null gate whose charge size are 0.8 mm×0.8 mm with different gap thicknesses are simulated by ANSYS/LS-DYNA software, and the simulation results are verified through experiments. The simulation results and experimental results show that an additional round air groove on the basis of traditional gap explosive null gate could contribute to shock attenuation and gap breakage. Gap window of the null gate for reliable action is increased from 0.6-0.7 mm to 0.7-1.0 mm, which improve the function reliability of gap null gate.