Multi-input converter combining various ambient sources, is considered as an effective approach to solving the problem of the sporadic and intermittent exist in energy harvesting. This paper proposes a multi-input variable structure to harvest vibration energy, which can work in dual sources parallel mode (DIPM), dual input series mode (DISM), and single source mode (SIM). In this work, GaN is adopted to eliminate power loss caused by body diodes of MOSFETs. The steady-state performance and input power of three modes are derived, it concludes that DIPM has the highest power which is different from traditional applications and DISM provides a wider working range. Due to the range of voltage variations in the energy harvesting process, the change of three modes can match the input and output power dynamically. Otherwise, the optimal power extraction strategy and energy management method based on impedance adjustment in discontinuous conduction mode (DCM) is used to improve the energy harvesting efficiency. An experimental prototype with simple control is built to verify the feasibility and performance of the proposed variable structure.