The poisonous gas in combustion gases for gun propellant by manometric bomb test was analyzed by infrared spectrum technique. The results show that manometric bomb test and infrared spectrum technique can be used to judge poisonous grade of combustion gases of various gun propellants. Evaluation method was put forward for propellant preparations. Combustion gases can be reduced when KNO₃,CuO and polyester are added in gun propellant formulation.