NOVELTY - Fish oil is used to prepare biological diesel by adding fish oil and 0.3-0.37 ml/g methanol into reaction container; heating in water bath at 50-550 degrees C; adding fish oil with 6-8 mass% concentrated sulfuric acid with stirring; reacting for 4-5 hours in water bath; quickly cooling at room temperature; standing and layering reaction liquid; discharging lower water phase; neutralizing upper layer solution; and contacting upper layer solution with anhydrous sodium sulfate to obtain separated fish oil with low acid value.    USE - Use of fish oil to prepare biological diesel.    ADVANTAGE - The method makes full use of aquatic product processing waste resource, provides biological diesel, relieves energy, reduces environment pollution, and has high production efficiency.    DETAILED DESCRIPTION - Fish oil is used to prepare biological diesel by adding fish oil and 0.3-0.37 ml/g methanol into reaction container; heating in water bath at 50-550 degrees C; adding fish oil with 6-8 mass% concentrated sulfuric acid with stirring; reacting for 4-5 hours in water bath; quickly cooling at room temperature using cold water; standing and layering reaction liquid for 2-3 hours; discharging lower water phase separated from sulfuric acid and methanol; neutralizing upper layer solution with distilled water at 50-60 degrees C; contacting upper layer solution with anhydrous sodium sulfate to obtain separated fish oil with low acid value; taking fish oil with low acid value with reaction container; heating in water bath at 50-60 degrees C; adding fish oil with 1.2-1.5 mass% sodium hydroxide and 0.31-0.35 ml/g methanol while stirring; reacting for 40-60 minutes after taking out from water bath; quickly cooling at room temperature using cold water; standing and layering reaction liquid for 2-3 hours; recycling lower glycerol; neutralizing upper layer solution with distilled water at 50-60 degrees C; contacting upper layer solution for 12-14 hours with 15% anhydrous sodium sulfate; and separating via centrifuge to obtain yellow clear and transparent biodiesel product.