In order to carry out the design and simulation of the seeker, the dynamic model of two frame seeker was established, and the source of seeker isolation was revealed. Firstly, the reference coordinate system was defined, and the kinetic equation of inner seeker head and outer frame was derived according to principle of dynamics. Secondly, combined with feedback control theory, the closed loop control block diagram of seeker was obtained through equation transformation. Finally, the isolation and coupling characteristics of seeker were simulated, and the validity of the model was verified. The results showed that the disturbance of the missile body entered into the close loop control circuit of seeker through the outer frame of weeker with two forms, which were geometric projection and disturbance torque, and it was the origin of isolation problem.