The invention discloses a biochemical fuel and a preparation method thereof. The raw materials of the biochemical fuel include, by weight percentage: 95.3 to 96.4% of lightweight oil, 2.5% of water, 0.025 to 0.05% of potassium hydroxide, 0.025 to 0.05% of sodium hydroxide, 0.3 to 0.6% of acetic ether, 0.55 to 1.1% of absolute ethyl alcohol and 0.1 to 0.2% of ferrocene. The preparation method includes 1, dissolving the potassium hydroxide and the sodium hydroxide in water of proper amount, and mixing with the acetic ether and absolute ethyl alcohol evenly; 2, weighing and mixing the lightweight oil with the residual water, stirring for 15 to 30 minutes, adding the material prepared in the step 1, and stirring for 10 to 15 minutes; 3, adding the ferrocene into the material prepared in the step 2, filling, and obtaining the finished products. The lightweight oil serves as the raw material, cost is low, the preparation method is simple, the heat value is high, impurity quantity is small, the combustion effect is fine, the exhaust is clear, safe and free of pollution, and the biochemical fuel is adaptive to power boilers, general boilers, catering industry and various burners consuming oil.