Virtualization technique is one core of cloud computing. For the virtualization security problem introduced by cloud computing, especially for the private cloud computing, a solution based on divide-conquer strategy is proposed. First, the security risks induced by virtualization are analyzed and classified, and then based on the divide-conquer idea, for each kind of security risk, some corresponding solutions are presented. Risks analysis shows that based on the proposed solutions in this paper, the security risks of private cloud computing virtualization can be reduced reliably.