The prevention of arc and electromagnetic interference(EMI) through physical separation is an important issue during the process of electrical wiring interconnection system(EWIS) design for commercial aircraft. Based on CST, this article sets up different types of the electromagnetic interference and simulates the types of cables and the electromagnetic interference between different signals through physical separation space. It is proved that physical separation can not only prevent the arc but also reduce the EMI. Using shielded and multi twisted cable can reduce EMI effectively.