The utility model relates to a formwork system of a diagonal wall insertion form. The formwork system comprises upright rods, transverse rods, diagonal bracings, a foot piece, a main keel, secondary keels, lower phenolic aldehyde laminated plywood, H-shaped steel and upper phenolic aldehyde laminated plywood. The upright rods and the transverse rods are connected with one another by a plurality of fasteners; oil supports are arranged at the bottoms of the various upright rods and are supported on the foot piece; the diagonal bracings are connected onto the fasteners; the main keel is obliquely arranged on the upright rods and the transverse rods, and the secondary keels are laid on the main keel; a steel pipe is arranged at each of joints of the upright rods, the transverse rods and the main keel; the lower phenolic aldehyde laminated plywood is mounted on the secondary keels; the H-shaped steel is welded with embedded reinforcing steel bars of building components; the upper phenolic aldehyde laminated plywood is mounted on the H-shaped steel and is parallel to the lower phenolic aldehyde laminated plywood. The formwork system of the diagonal wall insertion form has the various advantages of simple structure, convenience in mounting, firmness in fixing, reusability and the like, and is applicable to pouring diagonal wall concrete.