Well-defined Fe3O4/Mn OOH nanoparticles with 61.1 emu·g-1in magnetization intensity and 90.53 m2·g-1in surface area have been synthesized by a new-style of high-frequency impinging stream(HFIS)reactor.In this reactor,two streams first collided together to form nano Fe3O4suspension,which subsequently flew through an S-shaped main channel to generate high-frequency reversing high-gravity fields.At the same time,24 thin liquid sheets impinged into the main channel at the frequencies higher than 100 Hz to create nano Fe3O4/Mn OOH colloids.The obtained powders were characterized by transmission electron microscopy/energy dispersive spectrometer(TEM/EDS),X-ray diffraction(XRD),Brunner–Emmet–Teller(BET)and vibrating sample magnetometer(VSM).Experimental results indicated that low coating ratio prolonged the induction period of heterogeneous nucleation.The high-frequency impingements of 24 thin liquid sheets greatly accelerated the macro-mixing and the initial dispersion.The high-frequency reversing high-gravity fields promoted the mesoand micro-mixing.As a result,nano Fe3O4cores were fleetly and uniformly covered by Mn OOH precursor.As a continuously operated and static high-gravity reactor,the high-frequency impinging stream(HFIS)reactor is being developed to the large-scaled and low-cost production of various nanocomposites. Well-defined Fe3O4 / Mn OOH nanoparticles with 61.1 emu · g-1 in magnetization intensity and 90.53 m2 · g-1 in surface area have been synthesized by a new-style of high-frequency impinging stream (HFIS) reactor. streams first collided together to form nano Fe3O4suspension, which subsequently flew through an S-shaped main channel to generate high-frequency reversing high-gravity fields. At the same time, 24 thin liquid sheets impinged into the main channel at the frequencies higher than 100 Hz to create nano Fe3O4 / Mn OOH colloids. The obtained powders were characterized by transmission electron microscopy / energy dispersive spectrometer (TEM / EDS), X-ray diffraction (XRD), Brunner-Emmet- Teller (BET) and vibrating sample magnetometer VSM) .Experimental results indicated that low coating ratio prolonged the induction period of heterogeneous nucleation.The high-frequency impingements of 24 thin liquid sheets greatly accelerated the macro-mixing and the initial dispersion.The high-frequen cy reversing high-gravity fields promoted the mesoand micro-mixing. As a result, nano Fe3O4cores were fleetly and uniformly covered by Mn OOH precursor. As a continuously operated and static high-gravity reactor, the high-frequency impinging stream (HFIS) reactor is being developed to the large-scaled and low-cost production of various nanocomposites.