Abstract: An optimal procedure for electro-mechanical variable transmission equipped with a planetary gear trains was presented by classifying the connection scheme and calculating the split electric power. The equations of split electric powers which were general in describing the system characteristic were established. The power-split evaluations demonstrated that the input power-split configuration was applicable to hybrid-electric vehicles. The states of power-split and system efficiency according to the internal-combustion engine’s characteristic were simulated in Artemis driving cycle, and the results showed that the power-split planetary gear trains was a compact and highly efficient driveline solution for hybrid-electric vehicles.