The utility model provides a clamp device of an underwater adamas rope sawmill, which comprises a framework, a clamping part and a guide part. The framework is formed by jointing of four V-shaped gap mainboards and a connecting board; the clamping part comprises a clamping hydraulic pressure cylinder and a clamping piston, and a piston rod of the clamping hydraulic pressure cylinder is connected with the clamping piston and is arranged between a first mainboard and a second mainboard as well as between a third mainboard and a forth mainboard; the guide part is arranged on the first mainboard, and comprises a guide way and a guide sleeve, wherein, the guide sleeve and the guide way are vertically arranged and are corresponding to each other. The clamp device of the utility model has reasonable structure, is suitable for underwater operation mode and special requirement of environment, is used for large pipe diameter holding, can perform guide function for the cutting operation, and is suitable for the cutting operation of standpipes; simultaneously, a radial force of a transversely arranged part of the rope sawmill generated during the cutting process can be caused to finally act on the clamp device and the standpipes, thereby avoiding the deformation of transverse parts, and ensuring the normal operation of the adamas rope sawmill. The use effect is perfect.