The invention discloses a coal flotation agent. The coal flotation agent is prepared from the following materials in parts by weight: 100 parts of oil-containing sludge, 100-400 parts of water, 0.25-1.5 parts of emulsifying agent, 0.1-5 parts of viscosity reducer and 0-5 parts of foaming agent. Besides, the invention further discloses a preparation method of the coal flotation agent. The coal flotation agent disclosed by the invention adopts the oil-containing sludge as the materials, and is added with the emulsifying agent, the viscosity reducer, the foaming agent and water. The produced coal flotation agent is an emulsion type coal flotation agent, so that the flotation agent is easy to disperse in a water phase during a coal flotation process, and therefore, the collection efficiency is improved. The condensation point of the oil-containing sludge is higher, and the added pour point reducer can be used for lowering the condensation point of the oil-containing sludge, so that the oil-containing sludge is improved in mobility and convenient to disperse; besides a foaming effect and a foam stabilizing effect, the added foaming agent can be used for achieving the effect of a cosurfactant during a process of preparing the emulsion type coal flotation agent, and can be cooperated with the emulsifying agent to stabilize the emulsion; and the added water can be used for improving the proportion of a continuous phase, and therefore, the coal flotation agent is beneficial to preparing oil-in-water emulsion.