Static mixer is widely used in the process industry due to their advantages of compact structure, excellent intensification performance and continuous production. The enhancement mechanism of multiphase flow and dispersion mixing in Q-type static mixer (QSM) are not adequate, which restricts its application in green production of fine chemicals and green production of active pharmaceutical ingredient. The computational fluid dynamics (CFD) coupled with the population balance equation are used to simulate the flow and dispersion performance of droplets in the QSM. The discrete interval number of droplet size in the class method (CM) is set as 16 groups. The numerical simulation result in the classical helical static mixer has a good agreement with the experimental results. The dispersive mixing performance of different medium in RL-90-QSM are studied under Re=8000~24000. The effects of dynamic viscosity, interfacial tension, and phase volume fraction on the Sauter mean diameter (d32) are analyzed, respectively. The Q-type elements have good functions of splitting, recombination, and stretching. At higher Reynolds number and lower phase volume fraction, the average d32 values at different cross section obviously decrease in the first group of elements and then gradually decrease with the increase of mixing time. They become stable after z/l=10. The decreasing ratio of d32 at z/l=11.5 of benzene, toluene, cyclohexane and silicone oil 50 relative to the inlet droplet diameter (2.50 mm) are in the range of 78%~95%, 80%~96%, 73%~94% and 82%~96%, respectively. RL-90-QSM has the advantage of high efficiency and universality for dispersion mixing for the medium with different physical properties. The dispersion performance of droplets in liquid-liquid two phase flow with different continuous phase viscosities and discrete phase viscosities is similar. Compared with dynamic viscosity of discrete phase, the interfacial tension has much more influence on the final mixing result. As far as the restrained aggregation be concerned, the breakup performance of droplets is still predominant at dispersed phase volume fraction no more than 5%.