In this paper, an analytical model of permanent magnet brushless dc motors (BLDCM) coupled with inverter is proposed visa field-circuit coupled method. Firstly, the relationship between the motor supply voltage and the DC-link voltage is analyzed based on the modulation scheme and the operation period of BLDCM. Then, a total solution matrix containing the analytical relations of motor supply voltage, current and motor structure parameters is established to calculate the vector potentials and the currents simultaneously. As a result, the output torque is calculated accurately. The proposed model can consider the influence of the motor structure, such as slotting, spatial distribution of the windings, etc, and control parameters on the motor performance. Compared with the simulation results of the field-circuit coupled time-stepping finite element model and experimental results, the proposed model is with high accuracy and rapidity for the current and output torque calculation. Furthermore, based on the proposed model, the effects of the pole arc ratio, air-gap length, coil turns and lead angle on the average torque and torque-current ratio are researched, which can provide the guidance for the fast optimal design of the BLDCM system.