The invention discloses a preparation method of bottle flake master batch, and belongs to the technical field of preparation of spinning raw materials. The preparation method comprises the following steps: feeding a nano level toner and a polyester bottle flake into a high-speed mixing machine according to a weight ratio for mixing, and introducing into a stock bin to obtain a raw material; introducing the obtained raw material into a double-screw extruder from the stock bin for melting extrusion, filtering the raw material through a first melt filter and a second melt filter in sequence, enabling the raw material to enter a metering pump, metering by the metering pump, introducing into an extrusion die head, and enabling a polyester melt strap extruded from a spinneret plate hole in a spinneret plate of the extrusion die head to enter a cooling water tank, and obtaining a polyester strap; performing multichannel drafting on the obtained polyester strap in the cooling water tank to obtain a drafted polyester strap; and introducing the drafted polyester strap into a slicing machine for slicing to obtain the bottle flake master batch. Impurities can be effectively removed, and the problem of chromatic aberration caused by a difference between a polyester bottle flake and chemical fiber master batch in the prior art is solved.