The probe layout and attitude formula of an infrared earth sensor are presented. Then, a method for establishing the simulation model of the horizon sensor by using the Satellite Tool Kit (STK) is put forward. The established model is used for the dynamic simulation of the horizon sensor. The detection images are acquired. Finally, the satellite attitude is calculated by using the obtained images and the simulation results under different conditions are given. The method is helpful to the determination of the horizon sensor plan in the early phase of project development so that unnecessary repetition can be avoided.