Abstract: To predict the geometric operational range of an acoustic homing torpedo under different hydrological condition, this paper presents a method to determine geometric operational range by using sound ray density. This method is based on the Snell law of acoustic propagation in water. Different velocity gradients among linear layers in water are utilized to draw the sound ray chart, and a mathematical model of the geometric operational range is built. Furthermore, the geometric homing range is predicted with sound ray density, a prediction system of geometric operational range for acoustic homing torpedo is designed and the function of the system is realized through a system software. The sea trial demonstrates the prediction validity of the system.