Rail transit system has been considered to have a large energy harvesting potential, and to be usable to achieve self-powering for rail-attached electrical installations. Dowty retarder is a key device installed on the side of rails to assist train braking, which can be used as a carrier for kinetic energy harvesting. In this paper, a high-efficiency kinetic energy harvester (KEH) based on a railway Dowty Retarders (DRs) is investigated. This new KEH can accumulate the kinetic energy of a decelerating train using a novel vibration rectification mechanism. The current study comprises four main components: energy input module, motion transmission module, generation module, and energy storage module. The energy input module has a screw-nut mechanism that can convert linear vibration into rotational motion. As a core component of the entire device, the motion transmission module contains a special closed-loop shaped gear train that converts the two-way rotary motion into a unidirectional rotation. The final unidirectional rotation is transferred to the generation module for power generation and the generated energy is stored in the energy storage module. Finally, both experimental and simulation approaches were performed to verify the dynamics response of the KEH mechanism. The maximum efficiencies of 55.4% and 51.9% are obtained during the simulation and experimental analyses. It is validating that the KEH mechanism is promising and practical in self-powered applications for the heavy haul railway.