In a method for managing power of host computers using a control computer, the method generates a power management command, groups virtual machines installed in the host computers at a first time if the power management command is a first type, to obtain a first group of the virtual machines. The method further relocates the virtual machines in the host computers based on the first group of the virtual machines, and closes idle host computers. Closed host computers are powered on if the power management command is the second type, all the virtual machines at a second time are grouped, to obtain a second group of the virtual machines. The virtual machines are relocated into each host computer based on the second group of the virtual machines.