To solve the isolation problem of transmitting-receiving antenna in very-near anti-missile system, this research analyzed the equivalent model of AMC, which is made of high-impedance electromagnetic surface, and shows the relationship between its reflectance and phase offset. Then a novel method wa put forward to improve the isolation by the AMC and the experiments show that the method is able to make the isolation reach -80dB in a 200MHz band. So it has a good application value because of its simple structure and low cost.