This paper discusses the problem that the cracks the coating of aircraft result in the variation of the medium performance index and thus affect the stealthy performance of aircraft. By using Ansoft Designer based on MOM and resolution methods, the calculation and analysis of radar X-band frequency wave high frequency electromagnetic characteristics are done when the medium parameter variation caused by cracks appear on the coating sinter ferrite stealthy layer of a perfect conductor disc base. By using V polarization wave incidence and H polarization wave incidence in calculation and analyses, the result shows that the infection is obvious on the stealthy electromagnetic performance because of the coating sinter Ferrite medium performance variation caused by cracks in 8-12 GHz.