The invention discloses a nano light carbon agent and preparation method thereof. The nano light carbon agent is prepared from the following components in a certain proportion: carbon nano tube, titanium dioxide nano tube, chlorella, porphyridium, glutamine, alanine, histidine, NaHCO3 (sodium bicarbonate), KNO3 (potassium nitrate), KN2PO4 (monopotassium phosphate) and distilled water; the preparation method comprises the following steps: (1) respectively weighing the raw materials for later use; (2) respectively weighing the raw materials in the step (1) according to weight percentage, uniformly mixing the carbon nano tube, titanium dioxide nano tube, chlorella, porphyridium, glutamine,alanine, histidine, NaHCO3, KNO3, KN2PO4 and distilled water, regulating pH value by using sodium hydroxide, putting in a reaction vessel, adequately stirring, and reacting for 8-12 hours to obtain the nano light carbon agent. The nano light carbon agent is reasonable in formula, convenient to use, simple to operate and high in nutrition use rate, is ecological and environment-friendly, has no environment pollution and can be conveniently popularized and applied; the yield of crops and the quality of fruits are improved to the greatest extent; and the preparation method is easily implemented.