This paper deals with the development of simulation model for the horizontal launch at submarines in the preliminary design phase. The simulation model is composed of submarine motion model, cross flow force model in the bow of submarine, and weapon motion model In launch through torpedo tubes. Using submarine and weapon characteristics and simulation condition, it can simulate the exit velocity of weapon through torpedo tubes and reaction forces. It should be helpful for the analysis of the safe launch and design requirements in the preliminary design phase of a submarine or a weapon launched through torpedo tubes.