The invention provides a device for controlling pressure of a die casting machine and a method. The device is characterized by comprising a first ceramic electrode protecting tube (1), a first copper lead (2), a second ceramic electrode protecting tube (3), a second copper lead (4), a logic judging element (5), a connecting lead (6), a booster pump (7) and a power supply (8). The invention further provides a method for controlling the pressure of the die casting machine by using the device. In field machine modulation, operators have no need to input the boost time, so that the hidden trouble of advanced or delayed boost of the die casting machine caused by machine modulation through field staff experiences is prevented, and the mechanical performance of an inner flange and a rim of a wheel casting is effectively improved.