By comparing laminar and turbulent models, the flow regime of water-cooling plate with straight channels was researched; the results showed that the average velocities were different in channels, and it was improper to set the flow regime of all channels with laminar or turbulent. The highest different temperature of IGBT installing place of water-cooling plate would be 6~9 ℃ to IGBT precise model compared with uniform layout heat source. The exact temperature field and junction temperature of IGBT would be got with precise model, which helped optimizing channel structure and improving heat transfer efficiency.