NOVELTY - Copper-rhenium-magnesium-aluminum four-component catalyst, prepared by: (a) preparing a mixed solution of copper nitrate, magnesium nitrate, aluminum nitrate and chlorinated rhenium; (b) preparing a mixed solution (alkali solution) of sodium hydroxide and sodium carbonate; (c) adding the metal ion solution and alkali solution in a mixed container; (d) transferring the precipitate to a flask for crystallization; (e) filtering the crystallized precipitate, washing, transferring to a baking box and drying; (f) baking; and (g) reducing in the hydrogen flow before using the catalyst.    USE - The catalyst is useful for preparing 1,2-propylene glycol by direct hydrogenation of crude glycerin biodiesel.    ADVANTAGE - The method for preparing 1,2-propylene glycol with high yield of 69.2% by using the catalyst at the mild and environment friendly condition is highly efficient.    DETAILED DESCRIPTION - Copper-rhenium-magnesium-aluminum four-component catalyst, prepared by: (a) preparing a mixed solution of copper nitrate, magnesium nitrate, aluminum nitrate and chlorinated rhenium with certain concentration, controlling the concentration of copper ion, magnesium ion and aluminum ion in the solution as 0.025, 0.35 and 0.125 mol/l respectively, the concentration of rhenium ion is 0.0009 mol/l; (b) preparing a mixed solution (alkali solution) of sodium hydroxide and sodium carbonate with certain concentration, controlling the concentration of the hydroxide and carbonate as 0.8 and 0.25 mol/l respectively; (c) adding the metal ion solution and alkali solution in a mixed container in the ratio of 1:1, controlling the temperature of the mixed solution at 25 degrees C and the pH of the mixed solution is 9-10; (d) transferring the precipitate to a flask for crystallization for 20 hours at 120 degrees C; (e) filtering the crystallized precipitate, using deionized water for washing until the pH of the filtrate is less than 7, transferring to the baking box and drying over night at 80 degrees C; (f) transferring the dried sample to the muffle furnace, baking for 4 hours at 400 degrees C; and (g) before using the catalyst, reducing for 1.5 hours at 300 degrees C in the hydrogen flow and controlling the hydrogen flow at 40 ml/minutes, is claimed. An INDEPENDENT CLAIM is also included for using the prepared copper-rhenium-magnesium-aluminum four-component catalyst directly for preparing 1,2-propylene glycol by taking the crude glycerin biodiesel including water and residual alkali impurity as the raw material, comprising: (a) adding 20 ml of crude glycerin biodiesel, the mass concentration of which is 75% into a stainless steel high pressure reaction pot including the glass flask lining and adding 1 g reduced catalyst into glycerin solution; (b) sealing the reaction pot, using hydrogen for exchanging air in the pot and filling hydrogen with certain pressure and controlling the pressure of hydrogen at 20 MPa; (c) placing the reaction pot in an oil bath pot at 180 degrees C and reacting for 10 hours at blending condition; (d) after the reaction, cooling the reaction pot to the room temperature, centrifuging the reaction solution and recovering the catalyst; and (e) rectifying the centrifuged reaction solution, taking the fraction, the boiling point of which is 187.3-189 degrees C and counting the yield after determining by using the gas chromatography.