In order to meet the requirement of high precision warship navigation and improve the gyro drift estimation accuracy of inertial navigation system (INS), based on extended state observer (ESO) gyro drift estimation algorithm of INS is proposed. Firstly, the horizontal attitude angle ESO estimation algorithm is introduced, then based on attitude control equation of INS, the ESO estimation algorithm of gyro drift is deduced, and the quantitative analysis conclusion of the estimation error is given. Finally, the algorithm is simulated and verified. The result shows that the estimation method based on ESO can lead to fast, no overshoot and high precision gyro drift evaluation in a short time, and the estimated steadystate error is 10^-4(°)/h when ΔAx and ΔAy are 10^-5g. In a word, the method can improve navigation accuracy of INS.