Under jamming conditions, calculation of number of firing times about ground-to-air missiles firing at air-raid formations, which enter the launch area with different ways, is a puzzle that the antiaircraft forces should urgently desolve, but are lack of system research. To solve this puzzle, the models of missile actual launch distance and number of firing times at air-raid formation in jamming condition are established by an analytical method, then the calculation methods of residence time of the air-raid formation entering the launch area with rule flow and poisson flow respectively are also given. Finally, the feasibility and effectiveness of the models are illustated with a numerical example and some practical and valuable conclusions are reached, which can provide a reference for the shooting efficiency evaluation, the firing training and the amelioration of weapon system.