[Objective] The traction rectifier and the traction inverter are crucial components of train traction converters. The traction rectifier primarily consists of insulated gate bipolar transistor (IGBT), resonant circuit, DC-side capacitor, and other components. Its fault frequency is higher than that of the traction inverter. An open-circuit fault in an IGBT does not result in significant overcurrent or overvoltage, making diagnosis and protection relatively challenging. Therefore, this paper proposes an open-circuit fault diagnosis algorithm for the traction rectifier IGBT based on a mixed logic dynamic (MLD) model and adaptive thresholds. [Methods] Based on the working principle of the traction rectifier, an MLD model of the traction rectifier was established, and the grid-side current was estimated. The residual difference between the actual and estimated values of the grid-side current during single IGBT open-circuit faults was then analyzed. Finally, adaptive thresholds were designed for fault diagnosis, and the location of the IGBT open-circuit fault was distinguished based on the changes in the adaptive threshold. This led to the development of an open-circuit fault diagnosis algorithm for the traction rectifier IGBT based on the MLD model and adaptive threshold, enabling the diagnosis and localization of IGBT open-circuit faults. [Results] The MLD model was established based on the Matlab/Simulink platform, and the adaptive thresholds were introduced to verify the effectiveness of the proposed algorithm. Simulation results indicated that this fault diagnosis method can detect the open circuit faults of the IGBT within several hundred microseconds, accurately locate the faulty IGBT, and avoid misdiagnosis even in the presence of external interference. [Conclusion] The open-circuit fault diagnosis algorithm for IGBTs based on the MLD model and adaptive thresholds can quickly detect and locate faulty IGBTs. Compared to traditional MLD fault diagnosis algorithms, this proposed method effectively addresses the threshold selection issue for different IGBT open-circuit faults, offers high diagnostic accuracy, and demonstrates strong robustness to external interference.