The utility model relates to a precise plastic helical gear mould. The preciseplastic helical gear mould comprises a fixed mould and a movable mould, and is characterized in that the fixed mould comprises an installation plate, a stripper plate, a fixed mould plate and an embedded piece of a fixed mould chamber, and the movable mould comprises a movable mould base plate fixed by bolts, square iron, a substrate, a movable mould plate and an embedded piece of a movablemould chamber, wherein the movable mould plate is provided with a movablemould guide pillar, the movable mould guide pillar penetrates in a guide sleeve of the fixed mould plate, and the inner side of the square iron is provided with a bottom needle plate and a face needle plate fixed by the bolts, and a top pipe is arranged; and the embedded piece of the fixed mould chamber is fixed on the fixed mould plate, and the embedded piece of the movable mould chamber is correspondingly arranged on the movable mould plate. According to the precise plastic helical gear mould provided by the utility model, the molding difficulty of products is lowered, the molding defects of the products, such as poor gas exhaust, poor filling and poor meshing degree are solved, the product molding period is reduced, and the product processing efficiency is improved.