For ship angular flexure measurement based on the ring laser gyro units, a simplified attitude matching method has been proposed, where the Kalman filter observation provides direct measurement of the desired ship angular flexure plus the ‘relative attitude’ term. The ‘relative attitude’, insensitive to the gyro biases of each LGU, arises from the gyro bias difference and initial ship angular flexure. Additionally, considering its slow-varying characteristics, the angular rate of the quasi-static angular flexure should be modeled as random walks. Numerical simulations validate that the simplified attitude matching method can track both the slow-varying angular flexure caused by sunshine heating and the short-time large-magnitude angular flexure caused by factors such as helm’s operation. According to full-scale experiments in several actual ships, the proposed method can reach an accuracy of 20″.