based on the magnetic coupling theory，and an experiment instrument of the resonant magnetic coupled wireless

power transfer system is developed. The transmission characteristics of the system are visually observed under the

LED load. The high frequency equivalent resistance of the transmitting coil is measured. The condition of maximum

output power and the law of frequency splitting are obtained by exploring the relations between the output power and

the signal frequency，transmission distance，or load of the system. The results indicate that the trend-skin effect of

the high frequency coil is obvious; and the higher the frequency is，the greater the equivalent resistance. The resonant

characteristics of the magnetic coupled wireless power transfer system are not only related to the transmission

signal frequency and the inherent frequency of the receiver and transmit circuit，but also linked to their coupling coefficient;

the output power as well as the transmission efficiency is maximized at the optimal full resonance. Our design

experiment instrument can be generalized to measure the stable characteristics of RLC series circuits，and operate

stably. The experimental results are consistent with the theory.