Abstract: Microreactors are widely applied in fields including chemical synthesis, pharmaceutical production, and energy materials. However, passive microreactors are generally limited by inherent design constraints, such as significant pressure drops and a high risk of clogging, which restrict their practical application in reaction systems involving high-viscosity fluids and solid particles. To address these limitations, this study enlarges the microchannel dimensions to the centimeter scale and develops a novel active microreactor equipped with a motor-driven stirring shaft to enhance mixing. Suitable for high-viscosity and solid-particle-containing systems, this design offers superior mixing performance and high production throughput. Three impeller configurations were evaluated within a 100-mm-diameter flow domain: a 26-mm-high straight blade, a straight blade with baffles (incorporating four transverse baffles), and a propeller (with a 110-mm pitch). Through a combination of computational fluid dynamics (CFD) simulations and experimental validation, the effects of time, inlet velocity, and stirring speed on mixing performance were investigated using the segregation index (X_S) and mixing efficiency (η) as evaluation metrics. Simulations utilized the RNG k-ε turbulence model and the sliding mesh technique for a water/glycerin system, with a grid size of 1.5 mm selected via grid independence testing. Analysis of mass transfer enhancement mechanisms revealed that the straight-blade impeller induced a radial jet via localized shear; the straight-blade impeller with baffles suppressed circumferential vortices to redirect momentum into radial and axial flows; and the propeller created an axially driven through-flow ring. The mixed fluid reached the outlet fastest with the propeller (0.9 s), followed by the straight-blade impeller (1.2 s) and the straight-blade impeller with baffles (1.3 s). Subsequently, η rose rapidly before stabilizing. Overall mixing performance was ranked as follows: straight-blade impeller with baffles > straight-blade impeller > propeller. Quantitative analysis indicated that the straight-blade impeller reached a peak efficiency of 90.74% at 358 r/min, whereas the straight-blade impeller with baffles further improved the peak efficiency to 93.70%. Although the propeller exhibited the lowest efficiency at low speeds, its performance surpassed that of the straight-blade impeller at a high speed (956 r/min). Furthermore, simulations demonstrated that η decreased with increasing inlet velocity (from 0.1 to 1.0 m/s) due to reduced residence time. To validate these simulation results, a test platform was constructed using the iodide-iodate reaction (with c(H⁺) = 0.01255 mol/L). Experimental results confirmed the reliability of the simulations and demonstrated that stirring speed had a significantly greater impact on mixing effectiveness than inlet velocity; specifically, increasing the stirring speed from 0 to 280 r/min substantially reduced X_S from 0.978 to 0.268. This study demonstrates that combining centimeter-scale enlargement with forced mechanical shearing effectively resolves mixing challenges in high-viscosity systems, providing valuable theoretical insights and design criteria for industrial applications.