The invention discloses a vacuum die-casting system of a die-casting machine, which comprises the die-casting machine, a fixed-mold wallboard of a die casting mold, and a vacuum program control device of a die-casting system, wherein the vacuum die-casting system of the die-casting machine is arranged on the fixed-mold wallboard, the template of the fixed-mold wallboard of the die casting mold is provided with a channel, the outlet of the channel is connected with a vacuumizing device consisting of a vacuum pump, a negative pressure tank, a filter and a vacuum shut-off valve of the die casting mold by pipes; a channel leading to the center of the template of the die casting mold is connected with a casing pipe, the inner end of the casing pipe is communicated with a cavity of the template of the die casting mold, and a valve rod connected with a piston rod of an oil cylinder on the fixed-mold wallboard is arranged in a hole arranged at the outer end of the casing pipe. When carrying out die assembling on the die casting mold of the die-casting machine, by aid of the negative pressure produced by the vacuum pump of the vacuum die-casting system, the invention instantaneously extracts gases in the cavity and the pipe of the template of the mold, and closes the channel timely when the cavity is filled with molten metals, thereby preventing the molten metals from entering the vacuum pipelines so as to carry out die-casting molding on the molten metals in a vacuum.