The invention discloses a rotor assembly of a permanent magnet synchronous motor and a manufacturing method thereof, comprising a rotating shaft, a balance ring, magnetic steel, a carbon fiber sleeve, a rotor iron core and a flat key, and a first U-shaped groove is provided on the outer surface of the rotating shaft , the flat key is set in the first U-shaped groove, the rotor iron core is sleeved on the outer surface of the rotating shaft and the rotor iron core is in interference connection with the rotating shaft, and the balance ring is sleeved on the end of the rotating shaft and the balance ring is respectively connected with the rotating shaft and the rotor core in an interference fit, the magnetic steel is pasted on the outer surface of the rotor core, and the carbon fiber sleeve is sleeved on the outer surface of the magnetic steel and the balance ring, so The interior of the rotating shaft is provided with a first cylindrical shaft hole and a second cylindrical shaft hole connected to each other, and the first cylindrical shaft hole is larger than the second cylindrical shaft hole; the invention has simple structure, convenient installation, disassembly and maintenance, and is not easy Crushing, high pass rate, small size, less consumables, and less heat generated during operation.