NOVELTY - A supported Hangjin number 2 soil solid alkali catalyst for preparing biological fuel oil by cracking microalgae, is new, where soil is loaded with magnesium oxide (MgO) and the catalyst is obtained by adding MgO and soil into water according to weight ratio of 1:1-2:5, cooling after reacting at 50-100 degrees C, filtrating, washing and drying to obtain catalyst; or taking MgO/Hangjin number 2 soil solid alkali catalyst as carrier, and loading with potassium iodide (KI), where catalyst is made by adding MgO and soil into water in weight ratio of 1:1-2:5, cooling, filtrating, washing and drying.    USE - As supported Hangjin number 2 soil solid alkali catalyst for preparing biological fuel oil by cracking microalgae; and for preparing bio-oil by cracking microalgae (claimed).    ADVANTAGE - The catalyst exhibits high activity, high selectivity and low cost thereby reducing reaction temperature, and achieving biological energy with excellent performance. Using the method, dual-purpose microalgae with environmental management and high-value utilization is achieved. The method uses Hangjin number 2 clay mineral materials, which is widely available. The method allows easy production, provides product having large specific surface area, and high mechanical strength, and catalytic function. The method is simple, has low cost, uses reagent that is easy to separate and recycle, provides product having high activity and high selectivity for biological organic matter high-temperature cracking reaction. The method provides product having good biological fuel oil fluidity, high heat value, and low oxygen content. The method forms biological oil in high yield, with good quality, has reduced production cost, and wide application prospect.    DETAILED DESCRIPTION - A supported Hangjin number 2 soil solid alkali catalyst for preparing biological fuel oil by cracking microalgae, is new, where the Hangjin number 2 soil is loaded with MgO and the catalyst is obtained by adding MgO and Hangjin number 2 soil into water according to weight ratio of 1:1-2:5, cooling after reacting at 50-100 degrees C, filtrating and washing, and drying to obtain MgO/Hangjin number 2 soil solid alkali catalyst; or taking MgO/Hangjin number 2 soil solid alkali catalyst as a carrier, and loading with potassium iodide (KI), where catalyst is obtained by adding MgO and Hangjin number 2 soil into water according to weight ratio of 1:1-2:5, cooling after reacting at 50-100 degrees C, filtrating and washing, and drying to obtain a KI/MgO/Hangjin number 2 soil solid alkali catalyst. The solid alkali catalyst is ground after being dried, and then roasted for several hours at 200-1000 degrees C in a vacuum environment, and screened by a screen of 100-200 meshes after being cooled in a drying environment. An INDEPENDENT CLAIM is included for a method of using supported Hangjin number 2 soil solid alkali catalyst for preparing bio-oil by cracking microalgae, involving: placing the raw materials of microalgae and supported Hangjin number 2 soil solid alkali catalyst into a thermal cracking reaction device after being mixed according to the weight ratio of 10:1-2:1, taking nitrogen as a carrier gas, controlling the heating speed to 10-30 degrees C/minutes, heating up to 350-600 degrees C, taking out the gas produced in the catalyzing and thermal cracking process by the carrier gas, after respectively passing through a third cooling system of liquid nitrogen, dry ice and ice water mixture, cooling the gas-phase product to 5-60 degrees C, and collecting the liquid state bio-oil.    DESCRIPTION OF DRAWING(S) - The figure shows flow chart illustrating preparation of bio-oil by cracking microalgae.