The electromagnetic compatibility already becomes an important aspect in missile design, especially when designing wire distribution. Based on CableMod software, the simulation forecast method was used to study missile's electro magnetic compatibility (EMC) problem. How to establish a suitable simulation model for missile was discussed. The coupling between wires due to connected wires was analyzed. The missile body affects electrical field inside and outside. The calculation result indicates that after the wires of electricity and signal inside missile are twisted and screened, the crosstalk between them declines obviously. It was pointed out that using pipe instead of mantle can restrain electro-magnetic radiation and is good for EMC test.