This paper investigates several split tooth vernier machines (STVM) with different magnet arrangements. For all the STVMs, uneven flux modulation teeth structure is applied to achieve higher back-EMF and torque density based on multiworking-harmonic theory. The dual flux modulation effect is considered and analyzed for the STVMs with consequent-pole rotors and stator magnets. Key parameters including the distribution of flux modulation teeth and pole arc of rotor magnets are studied and optimized for the comparable models. At last, a new dual-consequent-pole split-tooth vernier machine with multiple working harmonics is proposed. The proposed machine has 45% higher torque density and 27% higher power factor than the regular split-tooth vernier machines, which is due to the optimized distribution of flux modulation teeth and the dual flux modulation effect.