The energy storage system（ESS） as an energy buffering unit can effectively suppress power fluctuation. A new energy management method of hybrid battery and ultracapacitor storage system based on smoothing control is proposed. In this method， batteries and ultracapacitors are used to compensate for the low-frequency components and high-frequency components of fluctuating power， respectively. Meanwhile on the basis of traditional threshold management method， ultracapacitor terminal voltage pre-control is presented， in which according to the charging/discharging mode and state of charge（SOC） of ultracapacitors， the output power references of batteries and ultracapacitors are modified to prevent ultracapacitors from stopping working when terminal voltage reaches limits. Finally， a PSCAD model is used to verify the validity of this method.