The problem of stabilizing steady gliding is very critical for an underwater glider, which is subject to many non-negligible disturbances from the aquatic environment. Traditional control methods like PID control, LQR control or torque control, can not provide simultaneously easy controller implementation and fast convergence speed for stabilization. In paper we propose a new nonlinear, passivity-based controller for the stablization problem. The controller is designed based on an approximation of a reduced model that is obtained through singular perturbation analysis, and consequently, it does not require full state feedback and is thus easy to implement. The local stability of the closed-loop full system is established through linearization. Simulation results are provided to demonstrate that the proposed controller achieves rapid convergence in stabilization.