Permanent magnet motor is attracted widespread attention due to the high efficiency and power density, but demagnetization caused by overheating can affect their lifespan and operational reliability. This paper focuses on the research of high-speed permanent magnet synchronous motors with forced air cooling, analyzes the air friction losses and the electromagnetic losses of the motor, improves the calculation accuracy by considering the influence of rotor surface roughness and axial cooling wind speed in the air gap on the air friction losses of the rotor; On this basis, finite element and thermal network methods are used to construct coupling analysis models for the electromagnetic field and temperature field of the motor. The experimental verification results show that the thermal network model significantly improves the accuracy of motor temperature field analysis and have the advantage of high computational efficiency; Finally, the validated model of the motor ventilation structure is used for optimization analysis, the results show that the ventilation structure with four hole channels has advantages in motor heat dissipation. The above research provides theoretical support for breakthroughs in motor thermal management technology and references for motor design and optimization.