The work aims to explore the effect and mechanism of grinding fluid containing hydrogen peroxide on the surface quality of aluminium alloy specimen in barrel finishing. Under the same conditions, grinding fluid containing different concentrations of hydrogen peroxide were prepared as liquid media to carry out barrel finishing and friction and wear experiments on aluminium alloy specimens. The surface roughness of aluminium alloy specimens before and after processing was measured. The surface morphology of aluminium alloy specimens before and after barrel finishing was characterized. The wear scar morphology of aluminium alloy specimens after friction and wear experiments was also characterized. The changes of surface elements on the specimens after friction and wear experiments were analyzed. The changes of hardness of aluminium alloy specimens with surface depth after barrel finishing was also analyzed. The decrease rate of surface roughness under the action of hydrogen peroxide was greater than that under the action of deionized water. The friction coefficient and wear amount under the action of hydrogen peroxide were obviously smaller than those under the action of deionized water and dry condition. When the initial surface roughness of the specimen was small, the effect of the grinding liquid containing hydrogen peroxide on aluminium alloy specimen was obvious in barrel finishing. Under the action of the grinding liquid containing 0.3% hydrogen peroxide, Ra decreased from 0.220 μm to 0.055 μm, and the decrease rate of the surface roughness was 74%. As a result, the grinding fluid containing hydrogen peroxide can effectively improve the surface quality of aluminium alloy specimens with lower initial roughness after barrel finishing. Because of the adsorption and wetting effect of grinding liquid on aluminium alloy, the aluminium alloy has a certain lubricity and cleanliness in the barrel finishing, and the friction effect will cause a certain tribochemical reaction on the surface of aluminium alloy. The hydrogen peroxide in the grinding fluid accelerates the corrosion oxidation reaction on the surface of aluminium alloy and pulls the oxidation products out of the surface in the form of particles. Barrel finishing hardens the surface of aluminium alloy and improves its mechanical properties.