The performance of Strapdown Inertial Navigation System (SINS) and Global Navigation Satellite System (GNSS) integrated navigation largely depends on the formulation of the error equations in polar regions. A key challenge lies in deriving a unified error model that remains effective across the globe. Addressing the limitations of traditional integrated navigation error models for UAVs during transpolar flights, this paper proposes an error equation and correction strategy based on the wander azimuth mechanization of inertial navigation systems. By introducing velocity error as an intermediate variable, the modified Psi-angle error formula is analyzed, reducing update cycles for integrated navigation filters. Furthermore, by examining the projection characteristics of the Psi-angle error state in the computer frame (c), a hypothesis is proposed: aligning the azimuth axis of the platform frame (p) with that of the true frame (t) allows the conversion from the platform frame to the computer frame. This approach resolves the issue of directly utilizing the Psi-angle error state to correct inertial navigation errors. The capabilities of SINS/GNSS integrated navigation in transpolar regions is evaluated through simulation, with results validating the effectiveness of the modified error model based on wander azimuth mechanization. This method avoids the mutual conversion of error parameters between different error models and mitigates filtering instability caused by such conversions, offering a robust solution for polar navigation challenges.