Abstract: The residence time distribution of impinging stream of water coming from two or four(nozzles) in a reactor with diameter of 300 mm and by height of 500 mm were measured respectively,and the(influences) of flow rate and number of nozzles were discussed in this paper.The experimental results show that the macro-mixing process in the reactor is improved obviously at the same flow rate when the number of opposite nozzles is added.The experimental data were correlated with front by-pass mixing model and combined model for calculating the residence time distribution,and the features of the two models were discussed.The calculated results show that the models can finely describe the residence time distribution in the impinging stream reactor.