In the strap-down inertial navigation system (SINS), if the angular rate is converted into angular incremental and the traditional coning error compensation algorithm based on the angular increment is used, the attitude calculation will have a decreased accuracy and increased calculation cost.To solve the problem, a coning error compensation algorithm that taking directly the angular rate as input was proposed.The concrete form of the three-sample-algorithm was given in detail.In order to further improve the accuracy and reliability, the algorithm was optimized under the condition of coning motion.The result of the proposed algorithm was compared with that of the analytical method by simulation under the condition of typical coning motion.The simulation result showed that the proposed algorithm is effective, feasible and has higher accuracy.