Abstract: Common mechanizations for submarine inertial navigation system (INS) involve problems of accuracy depressing, lack of north benchmark and so on. Aiming at this problem, a transversal strapdown INS mechanization is designed here, which is applicable to polar regions. The navigation reference framework of the transversal coordinate system is constructed. The navigation parameter transformations from the transversal coordinate system to the locallevel coordinate system are deduced. Moreover, mechanization of transversal strapdown INS is established, and then an error analysis for the transversal strapdown INS is performed. Through error analysis, periodic oscillating errors existing in that mechanization are determined, and damping technology applicable to that mechanization is proposed to reduce those errors effeciently. Finally simulation test is performed to validate the feasibility of this system in polar regions, as well as the performance of the damping technology.