Several kind of motion composition mechanisms are discussed,which may be applied in the inner-linked transmission train based on the hybrid-drive.The epicyclic gear train with two degrees of freedom（DOF）has two motion inputs and one motion output is suitable for this motion composition mechanism.The 2K-H kind is most commonly-used epicyclic gear train with 2-DOF,due to its relatively simpler structure,and three common types of this 2K-H kind are selected to discuss their torque and power balance features.The conclusions are as follows,the NGW minus mechanism is able to meet performance requirements of the motion composition mechanism,the WW plus mechanism is able to meet performance requirements on certain conditions,the differential mechanism commonly used in hobbing machine usually do not meet the performance requirements.