To find out the atomization characteristics of the direct jet nozzle in the subsonic-supersonic large velocity gradient shear mixing layer， a kind of direct injector used to inject fuel into shear mixing layer is designed and a fuel atomization test system is set up. The particle image velocimetry system （PIV） is used to measure the spray field in the subsonic-supersonic large velocity gradient shear mixing layer. The influence of different parameters on atomization characteristics is studied by changing the nozzle flow rate， injection angle and the number of injectors in the experiment. The spray field in the subsonic-supersonic shear mixing layer is analyzed by digital image processing technology to sum up the law of atomization. Experimental results show that the change of flow rate will increase the penetration depth and the droplet diameter corresponding to the peak distribution of the broken particles will gradually become smaller， thus improving the atomization effect. At the same flow rate， the atomization effect is affected by the angle change of the nozzle. The atomization effect of both downstream and upstream is better than that of the vertical injection. The injection height of the reverse injection is the highest， and the fuel will bump onto the wall with the increase of the flow rate. For downstream injection， the penetration length increases with the increase of angle. The effect of inverse injection can be obtained relatively well by observing the boundary of integrated fuel trajectory. At the same flow rate， the change of the number of nozzle has little effect on the atomization effect and penetration depth. The results provide the basis for optimizing the engine combustion chamber.