The traditional access control method is done before the access, and can not handle the new authorization requirements in the access process. It is not suitable for the cloud environment virtual network. Therefore, the UCON improved model is applied to the virtual access control of the cloud environment. The original UCON model is constructed, and the UCON model is improved from the file storage and authorization aspects in view of the drawbacks of the UCON model. For file storage, use GFS mode to store the file server, enhanced security privacy files through space transformation form; for authorization, the user trust degree as authorized by the objective and subjective conditions, combining trust measure strategy, according to the recommended trust and reputation to achieve the calculation of trust degree, trust only meet the conditions of the authorized user can get access to the virtual access control to add a line with the characteristics of the barrier for cloud computing, to achieve improved UCON model. The UCON improved model is applied to the virtual network of cloud environment, and access control is realized. The experimental results show that the proposed method can effectively implement the document access control, image access control and high access performance.