The invention discloses a novel clamp device and a fixing method for grouting risers of an ocean platform. The device comprises a support steel pipe of which one end is connected with a riser hoop; the other end of the support steel pipe is connected with a positioning hoop which has a cylindrical structure of which the cavity is formed by two fastened semi-circular steel plates and a duct frame steel pipe; the cavity is filled with a cement paste layer; the outer walls of the semi-circular steel plates are provided with grouting holes and returning holes; the grouting holes are welded with short pipes connected with a grouting pump pipe; and the inner walls of the semi-circular steel plates are provided with shear keys. The fixing method is to fill slurry in the positioning hoop so as to ensure the safety of the risers. The device and the fixing method can be widely promoted and applied in the field of oil exploitation, particularly the design of risers of the Nanhai sea deepwater duct frames.