Electromagnetic wave is widely used in radar detection, navigation and communication. The electromagnetic wave is emitted, and it is reflected back after encountering the target. The distance, velocity, angle and other information of the target are obtained by processing the echo information. This is the most commonly used processing method. The realization process of the method based on the scattered wave target detection is that when the electromagnetic wave propagates to the target boundary, it will continue to propagate outward with the convergent point on the target interface as a new excitation source. By receiving and processing the received scattered wave, the location information of the target can be obtained. Based on the Maxwell equations and scattering theory, the expression of the electromagnetic scattered wave in the frequency domain is guided and given. This method of target detection based on scattered wave has certain advantages in passive location, and small target recognition.