During the start-up of large induction motors, magnetic saturation and skin effect are highly prominent. This study investigates their transient electromagnetic and thermal performance via finite element simulation and analytical methods. An electromagnetic model accounting for the skin effect is established. Based on steady-state simulation to identify temperature hot spots, a local 3-D fluid-structure coupling temperature model is further constructed to simulate the temperature rise characteristics under motor start-up and brief overload conditions. The results show that during start-up, the peak current of Phase A winding is much higher than its rated value, and the transient magnetic flux density also significantly exceeds the steady-state level. Thermal distribution analysis indicates that the maximum temperature rise occurs at the rotor bar slot openings under transient conditions, while the stator windings exhibit the most significant temperature rise under thermal steady-state conditions. The simulation results are in good agreement with experimental measurements. Finally, the dynamic temperature rise curves and permissible operating durations under different overload scenarios are calculated. This study confirms that the proposed method can accurately predict the transient losses and thermal behavior of large induction motors, providing important guidance for optimizing thermal design and improving overload protection strategies.