The invention relates to a method for producing polypropylene fiber by using waste polypropylene plastic, comprising the following steps of: mixing more than two types of polypropylene regenerated materials with different melt indexes, carrying out blending and modification, controlling controllable rheology of polymer rheology by a molecular weight adjustment mode, controlling the melt index of the obtained blends to be 12 to 20g/10min, granulating to prepare the regenerated material particles of the polypropylene, and spinning by a one-step spinning-drawing process. The polypropylene fiber produced by adopting the method shows unique properties, greatly improves the spinning property of the modified regenerated plastic; the spinned polypropylene fiber product has good glossiness, less broken filament and loose looping yarn and improves the use value of the waste polypropylene plastic.