The invention discloses a material injection device of a die casting machine. The material injection device comprise a material cylinder and a plunger, wherein the material cylinder is used for containing molten metal liquid, the plunger is arranged in an inner cavity of the material cylinder, the material cylinder comprises a flat part and a gooseneck part which are in transition connection by an inclining part, the lowest point of the inclining part is lower than the lowest point of a material outlet of the gooseneck part, the plunger comprises a plunger head and a second plunger head which are connected by a plunger rod, a non-pressure chamber for containing the molten metal liquid is formed among the plunger head, the second plunger head, the plunger rod and the flat part, a pressure chamber for containing to-be-injected molten metal liquid is formed among the plunger head, the gooseneck part and the flat part, and a one-way flowing device is arranged between the non-pressure chamber and the pressure chamber, is sealed during material injection, and is opened in the plunger resetting process. The material injection device of the die casting machine has the advantages that the die casting cycle is short, the production efficiency is high, the qualified rate of products is higher, the heating temperature of the metal liquid is lowered, and the service life of a die and other parts is prolonged.