The present invention discloses a cyclohexane oxidation reactor and a use method thereof. According to the cyclohexane oxidation reactor, a multi-layer diversion cylinder is arranged in a reactor shell in a sleeved manner, the diameters of each diversion cylinder are different, the interior of the reactor shell is divided into a multi-stage annular region, water passing-through gaps are preserved between the bottom portions of each diversion cylinder and the reactor shell, the heights of the diversion cylinders are gradually decreased toward the outer side along the center, the diversion cylinder at the center is communicated to a liquid inlet, the interiors of each stage of the annular region and the diversion cylinder at the center are respectively communicated to a gas inlet, the annular region at the outermost layer is communicated to a liquid outlet, and the top portion of the reactor shell is provided with a gas outlet. According to the present invention, with the cyclohexane oxidation reactor, at least more than half of the liquid phase cyclohexane flows through the gaps between the bottom portions of each diversion cylinder and the reactor shell in the layer-by-layer manner, and at the most of not more than half of the liquid phase cyclohexane overflows from the top portion of the diversion cylinder in the layer-by-layer manner; and the flow condition of the cyclohexane in the reactor is improved, the selectivity of the process is improved, and the oxidation selectivity of the cyclohexane can be improved by 1.5-3.0% compared to the prior art.