NOVELTY - A composite solid alkali calcium aluminum oxide (Ca12Al14O33) catalyst comprises calcium oxide (CaO) and aluminum oxide (Al2O3) at a mass ratio of 4.5:1. The catalyst has a porous net-shaped structure having a surface area of 15.971 m2/g, a porosity of 0.4311, a volume of the pore of 0.045 cm3/g, and a bore diameter of 11.28 nm.    USE - A composite solid alkali calcium aluminum oxide (Ca12Al14O33) catalyst used for preparing biodiesel (claimed).    ADVANTAGE - The biodiesel yield is more than 98%, and the reaction time is shortened for 40-60 minutes. The catalyst is inexpensive, achieves fast and simple operation, and is environment-friendly.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) preparing the catalyst, comprising adding L-glutamic acid to calcium chloride (CaCl2) solution, where the mass ratio of CaCl2 to L-glutamic acid is 200:1-300:1; slowly adding to sodium carbonate solution with same molar ratio of CaCl2 after dissolving by stirring; suction filtering after 1-6 hours at 20-80 degrees C, respectively washing by distilled water and ethanol for 2-3 times, drying for 1-5 hours at greater than 100 degrees C to obtain calcium carbonate (CaCO3) with mesoporous structure, and roasting CaCO3 at greater than 400 degrees C for 1-4 hours to obtain CaO with mesoporous structure; and mixing the CaCO3 and aluminum hydroxide (Al(OH)3) at a mass ratio of 100:19, placing in a mortar for 10-120 minutes for grinding, mixing and roasting for 1 to 5 hours at greater than 400 degrees C, and drying; and    (2) preparing biodiesel heating composite solid alkali catalyst and catalytic waste vegetable oil at 60-65 degrees C, where the molar ratio of low-carbon alcohol to purified waste vegetable oil is 6:1-12:1, the cosolvent is 5-80 wt.% of the waste vegetable oil, the dosage of the composite solid alkali catalyst is 1-5wt% of the purified waste vegetable oil; and reacting for 40-60 minutes; and recovering solvent by rotary steaming, layering, and separating lower layer glycerol.