[Objective] This paper aims to address the insufficient research on the loss characteristics of direct drive permanent magnet synchronous motor (PMSM) under inverter power supply conditions. [Methods] A field-circuit coupled joint simulation model was constructed by establishing a PMSM vector control system in Simplorer and combining it with a two-dimensional transient electromagnetic field finite element model of the motor in Maxwell. The iron core loss and permanent magnet eddy current loss characteristics of a direct drive PMSM for an industrial mill under inverter power supply were investigated. [Results] With other inverter parameters kept constant, only the carrier frequency was varied, the results showed that the 5th and 11th harmonic amplitudes in the PMSM air-gap magnetic flux density, as well as the permanent magnet eddy current loss, decreased as the carrier frequency increased. Simultaneously, the peak magnetic flux density in the stator and rotor cores decreased with the rising carrier frequency, and the simulated iron loss also exhibited a downward trend. [Conclusion] Comparative analysis indicates that when the carrier frequency exceeds 5 kHz, the sensitivity of loss to frequency variation decreases. Therefore, 5 kHz is selected as the optimal carrier frequency for the field inverter. The theoretically calculated system efficiency shows good consistency with the measured operational efficiency of the mill, thereby validating the accuracy of the established theoretical model and analysis method.