Technical characteristics and specifications of a platform seeker were analyzed, and the Line of Sight (LOS)angle,the test methods of scale factor and accuracy,and the guidance system structure of a strapdown seeker were researched. First, the strapdown optical seeker model was established and an extraction method for the angle of LOS was proposed based on the technical characteristics of the platform seeker. Then, the characteristics and test methods of the scale factor for the strapdown seeker were analyzed, and a steady-state Kalman filter was used to filter the angle of Body LOS(BLOS). Finally, the “attitude + overload” autopilot combined with “integral approximation proportional guidance” were used to simulate strapdown seeker guidance and its control system . Test and simulation results show that when the angle of BLOS for strapdown seeker is greater than 0.289 °, the scale factor error is less than 7%, which meets the scale factor calculation results. Moreover, the strapdown seeker with the resolution of 0.0056 ° was less than the average variation of angle of BLOS to be 0.011°in one cycle, which meets the sampling update request and achieves the combating precision of 1 m of terminal guidance. These results demonstrate that large area array and high-resolution is an important guidance means of strapdown image seekers.