Abstract: The present disclosure discloses a high-speed motor and an assembling method. The high-speed motor includes an air duct housing, a rotor subassembly, a stator subassembly, a bearing sleeve subassembly, and a fan blade. A mounting ring coaxial with the air duct housing is arranged at the middle right part in the air duct housing; several air guide plates are uniformly distributed between an outer wall of the mounting ring and an inner wall of the air duct housing; a bearing sleeve mounting cavity, a bearing mounting cavity, and a stator mounting cavity being respectively arranged at a left part, a middle part and a right part in the mounting ring; the rotor subassembly is coaxial with the mounting ring and is mounted in the mounting ring in a horizontal direction. The present disclosure has the advantages of reducing the resonance, lowering the noise, and the like.