Abstract: Underwater acoustic ranging error usually deviated from Gaussian distribution, which brings about low-precision for the extended Kalman filter (EKF) tracking in range-only positioning and navigation. Assuming that the ranging deviation comprises Gaussian and non-Gaussian deviation, an improved EKF (IEKF) algorithm and initial position determining method are put forward. Simulation and lake trial are conducted, and the results show that IEKF could achieve better precision compared to conventional EKF.