Abstract: The influence of the trench structure of the power IGBT is mainly n-drift region conductivity modulation rather than the improvement of the channel resistance. To explain this question, the paper simulation tool Sentaurus TCAD, due to two structures of 600V Trench-IGBT and Planar-IGBT were used to simulate the breakdown, conducting and switching characteristics, especially in the conduction state. Result shows that the proportion of the channel region is very low and the number of excess carriers in n-drift region is far higher than that of the planar one, so the conductivity modulation is better. That is trench structure is the main factor of the improvement of the n-drift region. At the same time, the E _off- V _CE(on) trade-off curves of the two different structures were compared, and it is found that the Trench-IGBT has lower on-state voltage drop and lower switch loss.