The existing underwater single beacon location usually considers the underwater vehicle to establish the dynamics model in the two-dimensional motion state, but the underwater vehicle moves in the three-dimensional state actually. In terms of the characteristics of its three-dimensional motion, the water depth is taken as the new state variable, a new underwater single beacon location model is proposed based on the original five state variables, and the corresponding process noise model is established. The new underwater single beacon location model is compared with the traditional model with the simulation data, and the location precision to evaluate the two models is outputted with the Kalman filtering. The simulation shows that the new underwater single beacon location model can improve the underwater location precision of the underwater vehicle.