Abstract: To stabilize roof arches of rock tunnel,grouted rockbolts were wid ely used in the designs of supports of the underground tunnels. A proper design o f rockbolts should be based on a clear understanding of both the features of roc kbolt reinforcement and the mechanism of the rock roof arch structure. For this purpose the mechanism of forming a rock tunnel roof arch and reinforcement will be illustrated with the underground powerhouse in The Three Gorges Project.