For solving the problem of calculating two turn angle shooting parameter with predetermined encountering state, by considering with possible process of special trajectory and shifting torpedo velocity, a universal model which satisfied the requirement of different shooting mode was constructed, and a formulas concerning Newton iteration arithmetic was given. The correctness of the model and arithmetic was validated by numerical experiment; some conclusion indicated that the model and arithmetic could satisfy the requirements to calculate shooting parameter for straightforward, sound auto-guiding, wake-homing, salvo and target selection, etc.