In view of using the propellant charge in the torpedo launcher, this paper puts forward the mathematic model of interior ballistic with two periods by using the first thermodynamic law.

• 针对火药发射的特点,利用开口系统热力学第一定律的方法,建立了以火药为工质的鱼雷发射装置内弹道数学模型,并进行了计算机仿真。