Abstract: According to the problem of the terminal guidance with a strapdown seeker, the main reason of the disturbance rejection rate was analyzed. The proportional navigation guidance system (PNGs) with the disturbance rejection rate parasitical loop(DRRPL) was established, the uniformly asymptotical stability of PNGs was put forward based on Lyapunov stability theory for the time varying system, restrictions of stabilizing PNGs were analyzed with the passivity approach, and the effect of the disturbance rejection rate on the stability of PNGs was studied. The results show that the uniformly asymptotical stability of PNGs is stricter to realize than DRRPL, while the disturbance rejection rate caused by the imperfect decoupling is uncertain, and the positive feedback of DRRPL is more likely to make PNGs unstable in advance and cause a larger miss distance.