The invention relates to a manufacturing method of a plastic flowerpot. The manufacturing method is characterized by comprising the following steps of firstly, preparing plastic particle raw materials, plant powder fillings, a specific mixed material hot-melting and extruding device and a flowerpot injection molding mold; secondly, respectively putting the plastic particle raw materials and the plant powder fillings into the specific mixed material hot-melting and extruding device, carrying out pre-plasticizing to form pasty materials by controlling an unloading speed according to a certain raw material proportion, pushing the pasty materials into the mold, and carrying out pressure injection to form a flowerpot product. According to the manufacturing method, by utilizing the principles that the plastic particle raw materials and the plant powder fillings cannot be uniformly mixed after simultaneously entering a hot melting type screw rod extruder, the plastic materials are easily melted and the plant powder fillings are not easily melted, smooth surface parts and rough surface parts which are not uniformly distributed and in different sizes are formed at the inner and outer surfaces of the flowerpot product to form decorative textured patterns of the plastic flowerpot.