Aiming at the influence of coupling coefficient variation on the output voltage of a high-power LCC-S topology inductively coupled power transfer (ICPT) system, a synchronous three-phase triple-parallel Buck converter is used as the voltage adjustment unit. The control method for the three-phase current sharing of synchronous three-phase triple-parallel Buck converter and the constant voltage output ICPT system under the coupling coefficient variation is studied. Firstly, the hybrid model consisting of the circuit averaging model of the three-phase triple-parallel Buck converter and the generalized state-space average model for the LCC-S type ICPT system is established. Then, the control methods for three-phase current sharing of the synchronous three-phase triple-parallel Buck converter and constant voltage output of ICPT system are studied to achieve the multi-objective integrated control of the system. Finally, a 3.3 kW wireless charging system platform is built, the experimental results have verified the effectiveness of the proposed modeling and control method, and demonstrated the stability of the ICPT system.