The automotive wind tunnel, which is the reference of current national aerospace wind tunnel technology, has become an important means of automotive aerodynamic research. Based on one 1:15 scaled 3 / 4 open-type vehicle wind tunnel, according to jet theoretical knowledge, this paper mainly studies the effects of vertex generator toward the jet flow out of the nozzle by experiment method. Four sets of generators with varied angles were applied in the experiment. The steady characteristics of the flow inside the test section were analyzed to evaluate the stability and uniformity of the flow. The unsteady characteristics of the flow inside the test section especially inside the open jet flow out of the nozzle were also analyzed. For on the one hand, this directly affects the turbulence level of the flow. On the other hand this is related with the low frequency buffeting phenomenon which is special for open jet wind tunnel. According to the results’ analysis, the generators with angle of 4 degree were found have the best effect toward flow quality inside the test section. And then further studies of the reasons for the effects were carried out by CFD method. Thus we got the way of improve the flow quality inside the test section by nozzle optimization. The purpose of this paper is to optimize the nozzle for improving the unsteady and steady characteristics of a 3/4 open-type wind tunnel. This paper could provide a reference for the optimization of vehicle flow field in the wind tunnel test section.