The utility model relates to a hot forging device for a transmission shaft joint fork with a horizontal fork part in the technical field of forging forming. The hot forging device comprises a flat die used for the flat die flattening of a blank, a bending die used for the pre-forging bending of the blank, and a final forging die used for the final forging forming of a pre-forging piece. The bending die comprises a convex die and a concave die which are arranged in an up and down matching manner, wherein a working part of the convex die is provided with an arc-shaped convex cross section, and a working part of the concave die is provided with a trapezoid groove of which the shape is matched with the shape of the bottom of the pre-forging piece. Compared with horizontal open type die forging, axial blind holes can be directly forged in the transmission shaft joint fork manufactured by the hot forging device, follow-up machining processes are omitted, the consumption of burr metal is small, and the utilization ratio of material is 85%. Compared with vertical hot extrusion forming, the process of the hot forging device is convenient to implement, and is stable; and the dies are relatively simple and are low in manufacturing cost.