Abstract: In order to analyze effects of disturbance rejection rate on stability of guidance and control systems, a conception of seeker disturbance rejection rate transfer function was presented. Both models of disturbance rejection rate transfer function and parasitical loop of seeker disturbance rejection rate were established. Then the characteristic of disturbance rejection rate transfer function was analyzed using frequency domain methods, and with Routh criteria the effect of guidance parameter on the stability zone of the parasitical loop as well as the influence of guidance dynamics orders on crossover frequency were studied. With an infrared image seeker, the disturbance rejection rate transfer function and stability of parasitical loop were analyzed further. Finally, measures for improving the disturbance rejection rate were presented. The study shows that the parasitical loop may go unstable in the middle frequency region mostly. Improving the gain of the seeker's stability loop in this frequency region is crucial to the disturbance rejection rate level and the stability margins.