Traditional monitoring systems for railway axle box bearings face issues such as complex wiring, high maintenance costs, and limited flexibility, which hinder their application in the intelligent management of industrial equipment. Therefore, a variable reluctance energy harvester (VREH) based on a built-in variable reluctance generator (VRG) for double-row tapered roller bearings is proposed, aiming to provide continuous power support for sensors and wireless transmission modules in bearing monitoring systems, thereby facilitating the intelligent design of bearings. The VREH converts mechanical energy generated during bearing operation into electrical energy through the variable reluctance effect, powering the wireless transmission module. The wireless transmission module then sends signals to a mobile PC, enabling wireless signal transmission. The power generation principle of the VRG was validated through theoretical and simulation analysis. Key design parameters, including the number of coil turns, the distance between the coil and the toothed metal ring, and the core material, were tested and analyzed for their impact on the self-powering performance of the VRG. Wireless transmission experiments demonstrated that the VREH can operate stably in the railway axle box bearings, achieving efficient energy harvesting, providing continuous power support for the wireless transmission system.