The invention relates to the technical field of computer virtualization, and provides a method for establishing a VNC (virtual network computing) covert channel between a cloud management platform and a virtual machine terminal user. The VNC covert channel comprises a message transformation module, a message sending module and a message feedback receiving module. The message transformation module provides an interface for calling the channel and is used for transforming message contents into pixel data which can be identified by a message sending end; the message sending module is used for adding the message image pixel data into original communication frames of a VNC server and a VNC client and sending modified communication frames to the VNC client together; and the message feedback receiving module is used for capturing operation response of the user to a message window during channel display and sending the operation response to the message transformation module. Therefore, the method has the advantages that the channel transparent to a virtual machine system can be established only by modifying parts of functional source codes of the VNC server in a KVM (kernel-based virtual machine) virtualization cloud platform, and bidirectional interaction between the cloud management platform and the virtual machine terminal user can be realized.