The track forecasting model of TBM in the middle course is one of the key models in the system of missile defense, and is a basis for the commander to control the threat situation、carry on the battle programming and design the battle scheme. This paper first explains the common coordinates and their conversions used in the forecasting process; then puts forward the particular process and computing method of the relative parameter in the model. Finally, through the simulation analysis, the conclusion got shows that this method is effective and practicable in the project simulation, which provides a technique support for the task programming and battle scheme's establishment.