Special cutting device for wellhead casing pipe

The invention provides a special cutting device for a wellhead casing pipe. The special cutting device for the wellhead casing pipe comprises a top cone machine frame, a hydraulic motor drive assembly, a rotary central shaft transmission assembly, a nozzle assembly, a guiding rotary tensioning mechanism and connecting parts, wherein the top cone machine frame is composed of a cone end cover, a cone body and a cone bottom cover; the hydraulic motor drive assembly is composed of a micro hydraulic motor, a planetary reducer and a driving gear; the rotary central shaft transmission assembly is composed of a rotary central shaft, a tapered roller bearing, a driven gear, a driven rotary central shaft, an angle sensor and the like; the hydraulic motor drive assembly and the rotary central shaft transmission assembly are fixed to the cone end cover in a flanged connection mode; through holes communicating with a high-pressure mixed transportation pipe are formed in the middle part of the rotary central shaft transmis