The invention provides a ball-cage-free cardan joint and a vehicle front-drive transmission system, middle transmission system and rear-drive transmission system. The ball-cage-free cardan joint comprises an external star wheel and an internal star wheel arranged inside the external star wheel. A plurality of external ball paths are arranged on the inner wall of the external star wheel in the circumferential direction, a plurality of internal ball paths are arranged on the periphery of the internal star wheel in the circumferential direction, and the external ball paths on the external star wheel and the internal ball paths on the internal star wheel correspond to each other one to one and communicate with each other in a reversely-staggered mode to form the ball paths. Each ball path is internally provided with a rolling ball in a containing mode. The ball paths are divided into three sets, the first set of ball paths is the same as the second set of ball paths in number, and each ball path of the third set is distributed between one corresponding ball path of the first set and one corresponding ball path of the second set. The cardan joint is free of ball cages, the structure of the cardan joint is simple, and the strength of areas where the ball paths make contact is promoted.