Because strapdown seeker is fixed with the missile body, the disturbance of the missile body makes the location of the target in the image deviate from the theoretical location. In order to achieve stable target-tracking, the search scope must be expanded. But it is difficult to guarantee real-time target-tracking. This paper established a decoupling model of strapdown imaging seeker, then proposed an algorithm for decoupling the attitude of the strapdown seeker. Finally, by making use of the attitude information acquired from the strapdown inertial sensors, simulation results show the algorithm can improve the reliability of real-time tracking.