With the development of high-speed electrified railway, many serious power quality problems have arisen and caused widespread concern. In order to achieve comprehensive management of power quality, modular railway power conditioner (MRPC) has been applied to traction systems. However, due to the presence of multiple sub-modules (SMs). The reliability of the equipment is threatened as the number of SMs increases. In medium-voltage applications, system reliability can be improved by adding redundant SMs. However, when the redundant SMs are run out, the reliability of the whole system cannot be guaranteed. Therefore, a fault-tolerant method based on DC bus voltage regulation is proposed to improve the reliability of MRPC by modulation signal reconstruction. The proposed method not only achieves fault ride-through to maintain normal operation and improves the SMs voltage stress on the opposite converter, but also effectively improves the over-modulation. The effectiveness of the proposed method is verified by down-scale experiments.