The　key　technology　in　Energy　Management　System　of　Electric　Vehicle　is　researched　in　this　paper.　The　hybrid　power　system　constituted　by　the　battery　and　the　ultra-capacitor　can　combine　the　advantage　of　the　high　energy　density　of　battery　and　the　high　power　density　of　ultra-capacitor.　Firstly,　through　the　analysis　of　different　structures,　a　suitable　one　is　selected　for　this　system.　And　then　the　importance　of　Energy　Management　System　in　the　Electric　Vehicle　system　is　dissertated　in　this　paper.　Secondly,　some　theoretical　study　for　the　regenerative　brake　of　electric　vehicle　has　been　expressed.　Finally,　the　theory　was　verified　by　some　result　of　system　simulation　and　experiments.