Two classic ways of working of the hydra-mechanical power split CVT are studied.The efficiency formula of power-split is derived by definition

the power split ratio is studied

and the influence of different parameters on system efficiency is analyzed.The results show that

the parameters that influence system efficiency are the volume ratio e between the variable pump and the fixed motor and its efficiency

the locomotion parameters k of the planetary

transmission ratio and efficiency of a fixed axis gear.The conclusions offer foundation to choose the proper parameter

therefore the efficiency of the system will be improved.