The invention provides a powertrain for hybrid vehicles, and relates to the field of hybrid vehicles. As the powertrain system for hybrid vehicles utilizes a first planetary gear mechanism and a second planetary gear mechanism which are cooperated with each other, wherein a first sun gear rotates with a first input shaft, and a second sun gear and the first input shaft are independent to each other, and the second sun gear can realize different motion states to provide different transmission ratios passes through a first brake, a second brake and a second clutch, so that the powertrain is simple in structure, low in cost and more adaptable. Further, the second motor is connected to the input shaft through the second planetary gear mechanism, and the speed of the second motor can be reducedand the torque can be increased by the planetary gear mechanism to effectively reduce the size of the second motor or improve the acceleration performance of the vehicle.