In order to improve the mixing effect of polyurea spray airbrush, a novel mixing chamber of polyurea spray airbrush was designed based on impinging streams principle. The mixing chamber adopted two level impingement mix and respectively used two groups of T types and Y types. After the mixing chamber model was designed by the SolidWorks, we used FLUENT to simulate with the methods of convective heat transfer and the impingement mix of the cold and hot water in the mixing chamber and calculated the micromixing time that the fluid stayed in the mixing chamber. The results showed that under rational conditions, the more multiplicity the mixing stages and impingement modes of T types and Y types are, the better mixing effects the impinging streams mixing chamber will be. The main mixing zone of impinging streams mixing chamber is the impinging area. In the spray airbrush, the total staying time of the fluid is about 5.71 ms, which meet the requirements that some materials have the features of quick mixing. The micromixing time is less than 1 ms, so the mixing effect is very good.