The invention discloses an assembly method of an integrated medium-speed wind driven generator, which solves the problem of large size of a cabin of an existing wind power generating unit. According to the assembly method, two end cap bearing groups of a wind driven generator are designed into an inward concave structure, so that the axial connecting length of a rotor of the wind driven generatoris shortened, an insulated coupling (7) is installed on the tail side of a transmission chain of the power generating unit, the inward concave positions of end caps are fully used, and the length of the transmission chain of the wind power generating unit is shortened; a medium-speed motor has the characteristics of low rotating speed, short axial length and large shaft diameter of a rotating shaft, the rotating shaft of the wind driven generator is designed into a hollow structure by utilizing the characteristics, and an output shaft of a gearbox passes through a hollow shaft of the generatorfrom the front end and is reversely connected with the insulated coupling by virtue of a flange plate on the other end. According to the structure, the shaft current between a stator and the rotor ofthe motor is effectively blocked by utilizing the shielding effect of metal materials on an electromagnetic field, and additionally, a penetrating reverse installation mode is adopted, so that the problem of incapability of installing the insulating coupling on the integrated unit is skillfully solved.