Motivated by the problem that the position error of strap-down inertial navigation system (SINS) accumulates over time while a deep-diving human occupied vehicle (HOV) executes unpowered diving, this paper describes an online SINS error amendment method using range-only positioning. The proposed method can avoid the use of expensive ultra-short baseline (USBL) system that needs to be precisely calibrated and long baseline (LBL) system, which is hard to be calibrated and expensive in ship time to deploy. The proposed method utilizes only a set of acoustic ranges from submersible support vessel as measurement information and the SINS error model as process model, based on which the error divergence is eliminated using extended Kalman filter(EKF). Results of simulation show that SINS/Range-only can effectively amend the longitude and latitude error in SINS based on the proposed method.