This work presents a novel process of nano-Ni preparation by liquid reduction method without surfactant in a combined reactor of a rotating packed bed (RPB) and a stirred tank reactor (STR). The reaction mechanism of this process was studied, and the effects of different operating conditions including rotation speed, NaBH4 concentration, liquid volumetric flow rate, and liquid circulation time on the characteristics of the nano-Ni were systematically investigated in the RPB to control the morphology and average particle size of the prepared nano-Ni. The average particle size of the prepared nano-Ni can be adjusted from 42 to 130 nm by changing operating conditions, and the prepared nano-Ni with a face centered cubic (FCC) structure, an average particle size of 42 nm, and a particle size distribution of 30-60 nm was obtained under the optimal operating conditions. This research provides a novel pathway and theoretical basis for controllable preparation production of nano-Ni.