The invention provides a universal joint cross shaft, which can be used for reducing stress concentration on the root part of shaft heads of the universal cross shaft and enhance the structural strength of parts specific to the technical problem of easiness in causing fatigue fracture due to stress concentration of a universal cross shaft of a universal shaft coupling in the current field of heavy load and super heavy load. The universal joint cross shaft consists of a spherical base and the shaft heads which extend from four directions of the base, are connected with a bearing and are of consistent shapes, wherein an approximately conical transition stage and a conical transition stage of which the taper angle is 90 degrees are arranged between the bottom of each shaft head and the base; and on the section of the shaft, buses of the approximately conical transition stages are arc lines, and buses of the conical transition stages are straight lines. The universal joint cross shaft has the beneficial technical effects that after the structure is adopted for the universal cross shaft, the stress on the root part of the cross shaft can be reduced effectively, the stress distribution situation is improved, the fatigue fracture resistance of a product is enhanced, the manufacturability of the cross shaft can be enhanced, the construction period is shortened effectively, and the production cost is reduced.