When the transmitter of Multi-Orthogonal Signal Underwater Navigation System(MOSUNS) is installed on a moving platform, the rotation of the platform leads to positioning error. In order to solve this problem, the motion error modeling is carried out in this paper, the relationship platform motion parameters (translation rate, rotation rate, etc.) and the linear velocity difference between each transmitter element and the phase error is deduced, and the relationship between the positioning error of the MOSUNS and the platform motion parameters is further deduced. Based on the motion error modeling of moving platform, a rotation compensation algorithm was proposed to compensate the phase error caused by platform rotation, and then the positioning error was compensated. The motion error modeling is quantified by computer simulation, and the validity of the phase compensation algorithm is verified by simulation.