The three-dimensional simulation on the internal flow field of circle jet nozzle, equilateral triangle nozzle and square jet nozzle were performed by Fluent. The results show that the impact of jet nozzle shape to the internal flow field is large and the jet velocity gradually decreases from geometric center to the wall region; As the inlet pressure increasing, the reduction of centerline velocity of non-circle nozzle is slower than that of circle nozzle, and the equilateral triangle has the lowest reduction.