The invention relates to a mould structure for processing mechanical parts, in particular to a preforging mould structure for processing shaft fork stamp forgings. The preforging mould structure for processing the shaft fork part stamp forgings comprises a preforging upper mould and a preforging lower mould which are used for horizontally arranging a shaft fork part forging and pressing mould and is characterized in that: on the outer edge of the shaft fork part, mould joints of the preforging upper and lower moulds are positioned on the upper and lower symmetrical central surfaces of the part; and on the mould joint of an inner circle of a fork lug part, namely a U-shaped inner circle, the preforging upper mould is extended downward one circle, and the preforging lower mould is recessed downward one circle of the corresponding height. Due to the mould structure, under the condition of the same amount of the used materials, a cavity can be filled by metal conveniently, rejection rate of a forging is reduced, a flash width is smaller, a horizontal projection area is smaller, equipment tonnage can be reduced, the bearing load of the mould is smaller, the service life of the mould can be prolonged, and due to slight flash, materials and cost can be saved, and problems that blank is deflected and is not placed stably before can be solved.