Abstract: In view of the problem that transmission efficiency of small wireless charging devices changes with distance between transmitter and receiver, relevant factors of frequency splitting were analyzed according to mathematic model of wireless energy transmission system. Under the condition that resonant frequency and impedance parameters do not change when frequency splitting occurs, mutual inductance of two resonance coils can be reduced by adjusting radial distance of the two coils, so as to inhibiting frequency splitting phenomenon and improve transmission efficiency. Finally, experiments platform of wireless power transmission system of small size resonator was set up, and the experimental results show that the system can successfully charge the load with good transmission performance, which is suitable for small wireless energy transmission equipment.