The invention provides a copper-based methanol synthesis catalyst and a preparation method thereof. The method comprises: mixing the copper-zinc mixed solution and the first precipitant aqueous solution in parallel, controlling the pH to be 7-8, and standing for aging to form a slurry A ; Add the second precipitant aqueous solution to the soluble aluminum salt aqueous solution, control the pH to 7-8, and the temperature to 40-50°C, leave it to age to obtain slurry B; mix slurry A and slurry B, filter, and pass through the solid phase Washing, drying, roasting, molding treatment, that is, the copper-based methanol synthesis catalyst is obtained. The above preparation method has simple steps, strong controllability, wide sources of raw materials, and easy industrialization. The preparation method of the present invention can obtain a copper-based methanol synthesis catalyst with high catalytic activity and thermal stability, which is suitable for the synthesis of methanol containing CO, CO2, H2 The synthesis gas can produce methanol under the condition of low temperature and low pressure, and the catalyst of the invention does not need to be reduced before use, which is convenient for large-scale popularization and application.