The invention discloses a method for preparing a coal flotation agent by using animal and plant grease and waste oil, and belongs to the field of the utilization of renewable energy sources-solar energy and waste grease, the preparation of the coal flotation agent and the application thereof. The method is characterized by using the environment-friendly solar energy to realize the decarboxylation or cracking reaction of the animal and plant grease or the waste oil as the raw material under the photocatalysis action of the sunlight, UV-light or visible light through controlling the types of photocatalytic materials, so as to achieve the purpose of preparing the coal flotation agent with different ratios among hydrocarbon, fatty acid and ester materials. The method uses the clean renewable energy sources-solar energy, and recovers the waste oil, so that the high cost problem caused by using petroleum base diesel or kerosene as the flotation agent is solved under the condition of petroleum energy-lacked, energy-saved and consumption-reduced economic strategy development; the method has the advantages of no poison, no harm, low cost, economy, environmental friendliness and feasibility, reduces the coal flotation cost, overcomes the defects in the prior art, and can be widely applied to the field of the energy sustainable development.