Abstract: According to the shallow borehole dillig, low borehole forming rate and other problems of the soft seam, the casing drilling technology was applied to i mprove the borehole forming rate and borehole forming depth of the soft seam.According to the function requirements of the clamping mechanism in the casing drilling「 ig for the casing drilling, the paper introduced the features, structure composition and working principle of the clamping mechanism.With the calculation analysis on the clamping force of the clamping mechanism, the clamping capacity of the clamping cylinder and the breaking capacity of the breaking cylinder and with the finite element analysis conducted on the main structure parts, the results showed that the parameter selection and the structure design of the clamping mechanism component could meet the aplication requirements and could provide the guarantee to the relibility of the clamping mechanism and the integral performances of the casing drilling rig.