Abstract: The arithmetic of satellite phased array scanning was deduced and a simplified model for on board phased array scanning was presented.The arithmetic in this paper gave out the formula of computing the planar angle of satellite phased array scanning based on the satellite orbit and attitude,and during the flight the phased array kept pointing to targeted point.According to the simulation,the relationship between pointing precision and attitude precision is achieved,a simplified model of autonomous control is provided,and meanwhile,the validity of the arithmetic is proved.The arithmetic can act as a basis for on-board autonomous computation.