An electric variable transmission (EVT) for hybrid electric vehicles (HEVs) is investigated in this paper. With a special double rotor structure, the EVT splits and reintegrates the output power of the internal combustion engine (ICE) to run at its optimum working efficiency. However, the high electromagnetic coupling degree causes torque ripple and affects the dynamic performance of the EVT. After introducing the configuration and working principle, the torque mathematical model of the EVT in an ABC three-phase coordinate system is proposed to analyze the cause of this torque ripple. Besides, a finite element method-based (FEM) structural optimization design for reducing the torque ripple and improving the working stability is presented. The magnetic field distribution, induced voltage and torque property validate the rationality of optimization.