Abstract: To predict the acoustic homing torpedo’s geometric range under different hydrological condition, it is presented that a method which using sound ray’s density to determine geometric operation range. This method is based on the Snell law of the acoustic propagation in water. It utilizes the different velocity gradient among the linear layers, it is realized that drawing the sound ray picture and building the mathematical model about the geometric operation range. It predicts the geometric homing range through sound ray density. The result proves that this design has a good effect on the trial.