CFD-PBM coupling method was used to numerically simulate the breakup and coalescence process of dispersed phase oil droplets in Kenics static mixer. The discrete method was used to solve the population balance model, aggregation kernel and breakage kernel adopt Luo model and turbulent model respectively. A mixture-multiphase model and a realizable k-ε turbulence model were also used. First, by comparing three different initial particle sizes, the influence of initial particle size of the droplet difference on the results was excluded, and the accuracy of the simulation results was verified by comparing with the experimental data. Secondly, the influence of parameters such as Reynolds number, element numbers and element aspect ratio on the particle size of the droplet was analyzed, and the evolution rule of the particle size of the droplet was revealed during the flow of dispersed phase in Kenics static mixer. The results showed that the particle size of the droplet at the outlet of the static mixer decreased with the increase of Reynolds number, and then the critical trend appeared. The particle size of the droplet decreased faster at the first few elements position of the static mixer. The higher the Reynolds number was, the shorter the flow distance required for oil droplets to break to achieve a stable particle size. The number of elements had a significant effect on particle size only at low Reynolds number. At the same Reynolds number, the smaller the aspect ratio was, the smaller the outlet the particle size of the droplet was, and the shorter the flow distance was required to achieve stability. It can be seen from the contour diagram that the change of rotation direction of elements and fluid separation action were the important reasons for droplet breakage. In addition, this can also explain why the smaller the aspect ratio was, the better the emulsification effect was.