The invention discloses a plastic kitchen knife. The plastic kitchen knife comprises a plastic knife handle, a main plastic blade, an auxiliary plastic blade, fixing holes and fixing buckles. The plastic knife handle is made of polypropylene plastics. The main plastic blade is provided with a flat knife edge and is made of food-grade polypropylene, and the root part of the main plastic blade is fixed to the plastic knife handle. The auxiliary plastic blade is provided with a tooth-shaped knife edge, made of food-grade polypropylene and attached and fixed to the side face of the main plastic blade. The fixing holes are formed in the top of the main plastic blade and the top of the auxiliary plastic blade respectively. The fixing buckles penetrate through the main plastic blade and the auxiliary plastic blade and are arranged in the fixing holes. In this way, the compatibility of the plastic kitchen knife on various kinds of food materials is expanded, the cutting efficiency of the plastic kitchen knife cutting the foot materials is improved, the cutting difficulty is lowered, and the sharpness of the blade is enhanced.