Different from the traditional "cross shaft" type universal joint, the universal joint of the transmission shaft adopts the "slotted shaft" design scheme, and completes the universal hinge function through the combination of ball joint, straight shaft, roller sleeve, needle roller bearing and other parts, and completes the static sealing of the universal transmission pair through the rubber protective sleeve fastened on the nylon ball socket and ball handle at both ends respectively, and has the function of lifelong maintenance-free with one-time grease; The solution also reduces the number of two-disc bearings and replaces the cantilever structure with a closed ball joint, thus achieving a lighter weight effect and a smaller limit installation size.