In order to solve the energy consumption in the data centers with virtualization,the power efficient allocation of Virtual Data Centers was investigated which included three components,namely poweraware embedding algorithm,access policy and defragmentation algorithm.A poweraware embedding algorithm was proposed to allocate resources for Virtual Data Centers in treelike network topologies,and enforce an access policy on the incoming Virtual Data Centers requests to reduce fluctuations in the power expenditure.As requested Virtual Data Centers enter and leave dynamically,there will be resource fragment in the physical network.Therefore,a defragmentation algorithm was devised to migrate virtual machines away from underutilized physical machines.These algorithms were evaluated by simulation and proven effective to smooth and reduce power expenditure over time.