The technology of casing drilling is one of the effective methods to solve the problem of complex formation drilling. In view of the technical problems in the process of casing drilling， such as sticking in the annulus between the inner and outer tubes， complex load on the drilling string， high energy consumption， limited continuous running depth of casing， bit sticking in deep hole hot dry rock granite broken under the action of thermal stress， a continuous casing drilling mechanism with twin impregnated diamond bits is innovatively designed in this paper. Theoretical analysis shows that concentric rotary drilling with the twin bits produces small size cuttings to avoid sticking of both the inner and outer drilling strings， improve the stress state of the drilling tool and reduce the risk of breaking of the drilling tool. Compared with conventional casing drilling， the energy consumption of the inner bit is reduced by29.29%. The outer bit employs a high matrix with the staggered water port and reinforcement structure， which effectively avoids local circulation of drilling fluid and improves the continuous running depth of casing. The design of this mechanism provides a new idea for casing drilling technology.