Degree of hybridization (DOH) in hybrid electric vehicle (HEV) relates to the power match among the engine, motor and batteries, and directly influences the ultimate design cost and the market target of HEV. Aiming at Jiefang hybrid electric bus (HEB), the relationship between DOH and the design cost of HEB has been studied, and the relationship between the ultimate estimate economic returns, the return term of increasing cost of HEB and DOH was primarily discussed, and the study will provide the theoretical basis for the selection of DOH.