The invention relates to a gas engine rack die, in particular to a main core box of a gas engine rack die, characterized in that the main core box for a gas engine rack die is formed by mutually buckling a moving die and a stationary die, wherein the middle of the moving die and the middle of the stationary die are respectively provided with a moving die sand core cavity and a stationary die sand core cavity which mutually correspond; two sides of the bottom of the moving die sand core cavity are respectively fixed with one locating block; two sides of the stationary die sand core cavity are respectively provided with a slideway; the slideways on two sides are respectively matched with a slide block provided with a screw hole; two sides of the stationary die are respectively fixed with a fixed baffle provided with a through hole through which one bolt passes; and the bolt is matched with the screw hole arranged on the slide block. The invention has the advantages of peculiar structure, high manufacture efficiency, high precision and being easy for operation, prolongs the service life of the die, improves die size precision and satisfies volume production.