The cyclone separator is widely used for the dedusting process in industry to extend its application scope, a novel return micro-cyclone with a tangential inlet was constructed considering its small and convenient feature. The cyclone was constructed by 3D printing technology, and the experimental system was established. A 3D fluid dynamics (CFD) model was developed with RNG k–ε model and discrete random walk (DRW) model. Discrete Phase Model (DPM) was applied for dust particles of different sizes in the cyclone to investigate the swirl and separation flow. The transient flow field, the tail swinging phenomenon, the outer and inner swirling airflows can be detected vividly. The numerical method predicts the quantity percentage of dust well with the deviations of 0.92 %, 1.15 %, 0.88 %, 0.69 % and 4 % of the experimental data for PM10–20, PM20–30, PM30–40, PM40–50 and PM50–60 when the initial air velocity is 7.3 m/s. There are few dust particles in the exhaust pipe, which are mainly fine particles of PM10 with few particles of PM10–20 and PM20–30 when the initial air velocity is low. The phenomenon of the dust ring at the top region is significant and varies with the air velocity. Dust concentration in different sections can provide further references to optimize the cyclone structure.