The invention relates to a powertrain for a hybrid electrical vehicle, comprising an engine, a first motor, a second motor and a transmission device, said transmission device having a planet gear set with double planet gear ranks comprising a first planet gear rank and a second planet gear rank, said engine is arranged on one side of said planet gear set, said first motor and said second motor are arranged on the other side of the planet gear set, said first planet gear rank comprises a small sun gear, a planet carrier, a short planet gear and an outer ring gear, said second planet gear rank comprises a big sun gear, a long planet gear and the planet carrier shared with the first planet gear rank, said long planet gear meshes with the short planet gear and the big sun gear respectively.