In allusion to the efficient vibration energy recovery problem of a wheeled electric tractor, a variable stiffness spring was innovatively integrates into the research team's existing vibration energy feedback device and a method was proposed to match the device's resonance frequency with the road surface excitation frequency, thereby improving energy capture performance. Firstly, the range of road excitation frequency was analyzed based on the road grade and vehicle speed of the electric tractor. Subsequently, a nonlinear 10-degree-of-freedom dynamic model of the variable stiffness vibration energy feedback device was formulated. With the QR decomposition, implicit restart Arnoldi method (IRAM) and adaptive cross approximation algorithm (ACA), the modal frequencies of the device were solved, and the modal evolution law was analyzed by combining these methods with the finite element method. On this basis, the stiffness coefficient of variable stiffness spring was determined, and the frequency matching method for the variable stiffness vibration energy feedback device was proposed. Finally, fixed-frequency and swept-frequency bench tests were conducted to compare the energy capture performance of the fixed and variable stiffness vibration energy feedback devices. The results demonstrated that the variable stiffness spring structure significantly broadened the resonance band of the device, increased the maximum instantaneous output voltage to 52.2 V, and boosted the average output power and electricity generation by 34.4% and 42.8%, respectively, at the same time, it met the vibration reduction requirement for the battery pack. The above research can provide theoretical and technical support for the power supply of electric tractors and it was of great significance to promote the development of its energy-saving technology.