Aiming at the problem of the accumulation of inertial guidance error over time for ships at long voyages in deep and distant seas, this paper proposes a three-point correction algorithm based on the normal vector position model to estimate the gyro constant drift of the inertial navigation system. The mathematical model between the three-point calibration position error and the drift angle is established under the normal vector position model, the equations for the drift angle and gyro constant value drift are derived, and the comprehensive calibration algorithm is designed and realized under the external horizontal damping condition. Based on the simulation test results, the proposed three-point calibration algorithm is able to estimate the constant value drift of the gyro, which overcomes the limitations of the traditional three-point calibration of equal latitude and low speed conditions, and is globally applicable; Compared with two-point calibration, three-point calibration reduces the maximum value of positioning error and RMS by 58.89% and 54.94%, respectively.