Ferromagnetic metal foreign Bodies are one of the common interference objects in the actual operation of wireless power transmission systems. It indirectly affects the output characteristics of the wireless power transmission system by affecting the electrical parameters of the magnetic coupling mechanism. DD/BP structure is the most common type of magnetic coupling mechanism for electric vehicle wireless power transmission system. This paper takes DD/BP magnetic coupling mechanism as an example to analyze the influence of ferromagnetic metal foreign bodies on the coils' self-inductance and mutual inductance, and introduces the influence of ferromagnetic metal foreign bodies in different positions on the magnetic coupling mechanism of DD/BP based on the analysis of magnetic theory. An electromagnetic simulation model of the DD/BP magnetic coupling mechanism is built to simulate the electrical influence by using Maxwell. Ferromagnetic metal foreign Bodies are set in different horizontal or vertical position of the model to verify the correctness of the theoretical derivation. The simulation results show that when the ferromagnetic metal foreign body is on both sides of the DD/BP coil, it will increase the coil self-inductance and the mutual inductance between the coils, while at the junction of the two D coils, it will increase the coil self-inductance and reduce the mutual inductance between the coils. In the vertical direction, the closer the ferromagnetic metal foreign body is to the coil, the greater the influence on the self-inductance of the corresponding coil, and the closer to any coil the greater the influence on the mutual inductance between the coils.