In this paper, the performance and characteristics of two typical field modulated permanent-magnet machines (FMPMs), i. e. regular permanent-magnet vernier machine(PMVM) and dual permanent-magnet-excited machine (DPMEM), were compared and analyzed. Firstly, the structures of the two machines were introduced and their structural characteristics were summarized. Next, by deducing the general expressions of the two machines, i. e. no-load back electromotive force (EMF) and output torque, their working principles were revealed, and the "unidirectional field modulation effect (UFME)" and "bi-directional field modulation effect (BFME)"were compared. Finally, by finite element method (FEM), the performance of two machines was compared and analyzed, and the correctness of the general expressions was verified. The results of FEM simulation show that under the same size, number of stator slots and stator teeth, pole-pair number (PPN) of windings and rotor permanent magnets (PMs), turns of each coil, winding connection, electric load, copper loss and rotational speed, the DPMEM is superior to the regular PMVM in terms of PM consumption, back EMF, torque density, torque per unit volume of magnet, power factor and efficiency.