Spinning disc reactors are widely used in the process of intensification of micromixing such as the treatment of wastewater, synthesis of nanoparticles, and photocatalytic reactions, and the flow type transition of its surface liquid film has an important influence on the micromixing performance. The flow type transition of the surface liquid film of the disc was investigated by changing the rotational speed and flow rate, and the flow patterns were initially classified into unsteady (U), spiral flow type, transitional wave (TS), irregular wave (I) and reverse spiral wave (RS), and the regularity of the spiral wave was found by comparing the flow types with each other and deriving the existence range of the spiral flow type. The micromixing performance of the spinning disc reactor was investigated under the spiral flow type by using the iodide-iodate reaction system to characterize the microscopic mixing performance with the dissociation index (XS), and the influence of the disc rotational speed, flow rate, viscosity, flow ratio and H+ concentration on the micromixing effect of the spinning disc reactor was investigated. The improvement of micromixing performance was limited by increasing the rotational speed, and when the rotational speed increased to a certain value (ω=125.6 rad/s), the improvement of micromixing performance was limited by continuing to increase the rotational speed. Decreasing the viscosity of the liquid, decreasing the flow ratio of the liquid, and decreasing the H+ concentration were all beneficial to improve the micromixing performance of the reactor. The results of the study provide a reference for the application and optimization of the spinning disc reactor in micromixing reactions.