Wireless power transmission technology is the key technology that enables special robots to achieve lightweight sustainable work. The magnetic coupling resonant wireless charging, must consider the impact of metal obstacles on the transmission system. The metal eddy current effect is equivalent to mutual inductance coupling circuit, and the transmission system is modeled by coupling circuit theory. The transmission equation of voltage gain coefficient and the expression of energy loss of metal obstacles to transmission system are derived. With the change of coupling coefficient, the transmission system still has frequency splitting, critical coupling, over-coupling and under-coupling. Given the parameters of the transmission system, the critical coupling coefficient Kc=1.54×10-4. When there are metal obstacles, K′c=1.09×10-2. which lead to the reduction of voltage gain, the shift of resonance frequency, the increase of coupling coefficient and the decrease of coupling performance in wireless transmission system. The change of output voltage in the presence of metal barrier is obtained by simulation.