In order to prolong the driving range long-trip driving cycle and the life cycle of batteries, Fuzzy control is presented with the purpose of enhance the performance of dual-energy electric vehicles applications.The dual-energy source consists of battery and ultracapacitor (UC). The ultracapacitor in dual-energy electric vehicles by bi-directional Buck-Boost cascade converter is employed as the feedback and the supplement of the DC bus energy in different working conditions of the vehicle. In this paper the fuzzy control method is employed for controlling the power flow of UC by supplying a transient power demand. Simulation results have proved that the control method has a good dynamic performance, and is applicable and effective for electric vehicle.