To restrain the accumulated navigation error of shipborne grid inertial navigation system (INS), the paper proposed a comprehensive calibration method based on grid frame to estimate and compensate the gyroscope constant drift. First, the P equation was derived based on grid frame, and the P equation established the relationship among the position errors, the grid yaw error, and the platform drift angles ψ. Then the ψ equation was derived to establish the relationship between the gyroscope constant drifts and the platform drift angles ψ. Finally, on the basis of P equation and ψ equation, a two-point comprehensive calibration scheme was designed, and the gyroscope constant drifts in body frame were estimated and compensated by establishing the relationship between the gyroscope constant drifts and observation errors. Under external level damping state, the gyroscope constant drifts were estimated after obtaining two intermittent external position and azimuth information, then the comprehensive calibration of shipborne grid INS was realized by resetting the position errors and grid yaw error and compensating the gyroscope constant drifts. Simulation results demonstrate that with the aid of two intermittent external position and yaw information, the proposed two-point comprehensive calibration method can estimate the gyroscope constant drifts accurately. Conducting the gyroscope error compensation and the system reset can efficiently restrain the accumulated errors of shipborne grid INS, thus significantly improve the navigation accuracy of ships navigating in polar regions.