The strong RFI (Radio Frequency Interference) on the ground or space around the radio telescope may make the receiver system in a nonlinear state. In order to reduce the influence of strong RFI and improve the efficiency of astronomical observation, a method of avoiding strong RFI based on telescope in far field is proposed in this paper. First of all, based on the far-field pattern of the radio telescope determined by simulation analysis, combined with the position relationship between the telescope and the interference source, the power response of the strong RFI reaching the focus of the radio telescope is analyzed. According to the performance parameters of the second-order intermediate frequency amplifier of the receiver, the calculation method of the avoidance angle of the radio telescope in the unsaturated state is determined. Secondly, this method is used to calculate and analyze the influence of civil aircraft on the radio telescope. For an active interference source on the civil aircraft without reflection and other propagation phenomena, the influence on the radio telescope can be effectively reduced when the main beam axis of the radio telescope deviates from a certain direction.