A double-joint sickle knife for an endoscopy therapy includes a knife head, a knife base, a knife body, an outer sheath, a guide wire, a handle and a sliding rod. The knife head is connected with one end of the knife base by a transverse joint, and the other end of the knife base is connected with a head end of the knife body by a longitudinal joint. The outer sheath is sleeved on the outside of the knife body and capable of sliding along the knife body. The tail end of the knife body is connected with one end of the handle, and a sliding rod for adjusting the transverse joint is arranged on the handle. The guide wire is electric conductive. One end of the guide wire is connected with the knife head, and passes through the knife base, the knife body, the handle and the sliding rod successively. The other end of the guide wire is connected with the power port.