In this paper thermal behavior of a 600kW 4200r/min interior permanent magnet synchronous motor (PMSM) with forced ventilation in the stator was analyzed using Fluent. Due to its high power density and compact structure, accurate thermal analysis of PMSM traction machine is of great importance in designing and optimizing. Different structures of stator ventilation are evaluated and the square ventilation structure in the inner surface of house is selected.