Abstract: A Position estimation algorithm for underwater vehicle is proposed based on the USBL/Doppler to cope with position feedback delay due to the underwater acoustic positioning system. The Kalman filter structure with the state equation and observation equation is established according to the navigation system for underwater vehicle. Moreover, the theory of adaptive Kalman filter is incorporated into the algorithm in order to enhance the estimation precision and make the system insensitive to the environment and initial conditions. Simulation result verifies the validity of the algorithm and conclusion is provided at the end of the paper.