This paper addresses the issue of reduced reliability in IGBT power modules of railway traction converters due to thermal stress. It investigates junction temperature modeling and active control based on multi-mode modulation. First, a junction temperature estimation model for IGBT power modules under multi-mode modulation conditions is established, including power loss calculation and thermal network equivalent circuit modeling, to accurately monitor the device junction temperature. Then, an active junction temperature control strategy under multi-mode modulation is proposed, which achieves active regulation of the junction temperature by real-time monitoring of the IGBT junction temperature and dynamic adjustment of the modulation mode. Simulation results demonstrate that the proposed method effectively reduces the peak and fluctuation amplitude of IGBT junction temperature, lowering the maximum junction temperature from 132 ℃ under uncontrolled conditions to approximately 110 ℃, a reduction of 22 ℃. Additionally, it reduces rapid fluctuations in junction temperature, significantly alleviating device thermal stress and enhancing the safety and reliability of system operation.