NOVELTY - Making magnetic nano bifunctional solid alkali catalyst involves taking ferric trichloride hexahydrate and ferrous chloride tetrahydrate, dissolving in distilled water to obtain solution A; adding solution A into chlorine zirconium oxide octahydrate and stirring; adding ammonia water in reaction system, stirring, standing and aging, absorbing colloid coagulation, filtering, washing and drying to obtain magnetic gel carrier zirconium hydroxide-iron oxide; and putting obtained magnetic gel carrier in container, adding potassium hydroxide, stirring, washing and drying to give product.    USE - For the preparation of magnetic nano bifunctional solid alkali catalyst i.e. K/ZrO2-Fe3O4 (claimed) which is used in making biological diesel oil.    ADVANTAGE - The method has low cost; and is easy to industrially popularize. The obtained magnetic nano bifunctional solid alkali catalyst has high reaction activity, good dispersing effect in the liquid phase, and faster reaction speed.    DETAILED DESCRIPTION - Preparation of magnetic nano bifunctional solid alkali catalyst, involves (i) taking 9.731 g ferric trichloride hexahydrate and 3.5786 g ferrous chloride tetrahydrate, dissolving in 200 ml distilled water to obtain solution A, (ii) adding obtained solution A into chlorine zirconium oxide octahydrate (ZrOCl2.8H2O), where the molar ratio of Zr and Fe is 15:1, taking non-intermittent and stirring for 1-2 hours; (iii) adding ammonia water in reaction system using dropping funnel to make pH at 11, stirring for 1-2 hours, and then standing and aging for 1-3 hours with magnet at the bottom of the reaction container, absorbing colloid coagulation, filtering, and using distilled water repeatedly washing until the pH is neutral, drying to obtain the magnetic gel carrier zirconium hydroxide-iron oxide (Zr(OH)4-Fe3O4), (iv) putting magnetic gel carrier Zr(OH)4-Fe3O4 in the container, according to a quantity of 10-40%, adding potassium hydroxide (KOH) in a mass fraction of 10-30%, stirring uniformly, standing for 2 hours, then washing using water, then drying in the muffle furnace at 500-800 degrees C for 2-5 hours, cooling to room temperature to obtain the magnetic nano bifunctional solid alkali catalyst i.e. K/ZrO2-Fe3O4.