Abstract: The microfluidic inertial impactor can be used as the first-stage filtration device in the filtered containment venting system (FCVS). This equipment can separate radioactive aerosols from the flowing medium passively, enabling rapid depressurization of the containment and initial filtration of radioactive aerosols after severe accidents. Thereby, the safety and stability of FCVS operation can be improved by reducing the total amount of aerosol filtration in subsequent equipment. In order to investigate the filtration behavior of aerosols in the inertial impactor, a visualization experimental device with a transparent observation window was designed. This device was utilized to conduct visualization experiments that focused on studying the deposition distribution of aerosols within the inertial impactor. Furthermore, tests were performed to evaluate the inertial impactor’s aerosol filtration efficiency and dust holding capacity. The experiment utilized the isokinetic sampling method and membrane weighing method to measure the aerosol concentrations upstream and downstream of the inertial impactor, both before and after filtration. Furthermore, to account for potential interference caused by aerosol interception and adsorption by the inner walls of the experimental section, the correlation ratio of the filtration system was also measured. Comparison of the experimental results with the corresponding numerical simulations reveals that the deposition distribution of aerosols observed in the visualization model accurately reflects the airflow patterns and the trajectories of the particles within the inertial impactor. Furthermore, the visualization experiments suggest that the majority of the aerosols are deposited on the upper surface of the filtration unit and the inner wall of the microchannel, demonstrating a filtration efficiency of over 60%. These findings validate the structural design of the microchannel inertial impactor and support its suitability for efficient aerosol collection. Based on the research findings regarding the cumulative effect on filtration efficiency over time, it is evident that continuous filtration leads to the gradual accumulation of aerosol particles on the surface of the filter unit of the inertial impactor. Simultaneously, there is a continuous increase in the number of particles adhering to the inner wall of the microchannel, which can result in changes in the surface characteristics of the impactor channels. Thus, it can be concluded that, under dust-holding conditions, the aerosol filtration efficiency of the inertial impactor will progressively improve as more aerosol particles are deposited. However, when the airflow velocity within the inertial impactor surpasses a critical value, the re-entrainment of high-speed gas flow onto the deposited particles causes a decrease in aerosol filtration efficiency due to particles re-suspension.