Rectangular jet is common in many engineering situations.To predict the flow field near the nozzle precisely is of great importance because it decides the development of the whole flow field.Although a series of studies have been carried out

it is not very easy to know the flow field clearly due to the complexity of rectangular jet.A large eddy simulation was conducted to investigate the flow field near the nozzle of a rectangular jet with Re=11435.The saddle shape of velocity was proved by simulation.Self-similarity flow mechanism of the streamwise velocity was shown on the central plane of y=0 when x>6De.The flow field of rectangular jet was similar with a round jet when x>8De.The simulation results fitted well with experiments.