The micromixing performance of two inline high shear mixers (HSMs) was studied using the iodide iodate reaction system, considering the effects of rotor speeds, flux ratios, viscosities and fluid concentrations. The segregation index (Xs) was adopted to assess the micromixing performance. It is indicated that the value of Xs decreases with the increase of rotor speed and the flux ratio of two feed solutions. The dual rows ultrafine-teethed HSM exhibits the poorer micromixing performance at low rotor speeds, comparing with the single-row blade-screen HSM. Then we modified the geometric configurations of the teethed HSM with the aid of computational fluid dynamics (CFD) analysis, including the modification of the clamp nut with blades and the addition of a liquid distributor, and reevaluated the micromixing performance in the modified HSM in order to improve mixing in the reactor. The results indicate that the fluid dispersion and turbulence intensity in the inlet region of the HSM play an important role in enhancing the micromixing level, the liquid distributor can greatly improve the micromixing performance of the dual rows ultrafine-teethed HSM and the estimated micromixing time can reach 10(-5) s. The results obtained here will provide much insight for the applications of the inline HSMs and other reactors in the field of intensifying fast chemical reaction. (C) 2017 Elsevier B.V. All rights reserved.