In order to improve the launching accuracy, launching stability and launching safety of the vehicle-mounted air defense system launching on the move, the excitation of random road surface, missile counterforce and impulsive force of combustion-gas flow, artillery counterforce must be comprehensive consideration. Based on the power spectrum density of road, using an harmonic superposition method to create three-dimensional randomly road model and to verify it. Simulation analysis and research are carried out on the road surface with national standard by multi-body dynamics method. The safety envelope interval of the air defense weapon system is obtained. Research shows that it's safe to launch under the condition of specified road surface and vehicle speed. Keywords: launch on the move; power spectral density; harmonic superposition; launching safety