Abstract: To improve the accuracy of field current calculation, coupling characteristic of permanent magnet field and excited field of consequent-pole permanent-magnet (CPPM) brushless DC generator(BLDCG) was analyzed based on finite element method, and the commutation characteristic of winding current with diode rectification is discussed in this paper. Moreover, formulas of field current were derived in view of coupling characteristic and commutation characteristic. Experimental results verify the theoretical analysis method.