The present invention relates to a double-joint sickle knife for an endoscopy therapy. The knife comprises a knife head (1), a knife base (2), a knife body (5), a guide wire (15), a handle (7) and a sliding rod (8). The knife head (1) is connected with one end of the knife base (2) by a transverse joint (3), and the other end of the knife base (2) is connected with a head end of the knife body (5) by a longitudinal joint (4). The outer sheath (6) is sleeved on the outside of the knife body (5), and capable of sliding along the knife body (5). The tail end of the knife body (5) is connected with one end of the handle (7), and a sliding rod (8) for adjusting the transverse joint (4) is arranged on the handle (7). The guide wire (15) is electric conductive. One end of the guide wire (15) is connected with the knife head (1), and passes through the knife base (2), the knife body (5), the handle (7) and the sliding rod (8) successively. And the other end of the guide wire (15) is connected with the power port (10). By means of the knife, a multi-angle movement of a cutting knife blade of the endoscopy knife can be achieved, wherein the movement includes a circumstance cutting by the knife blade in parallel with mucosal tissues. And the knife blade angle is not limited by the lens of the endoscope, so that the speed and the quality of the endoscopy therapy are greatly improved, and subsidiary injuries potentially occurring to peripheral tissues are minimized to the furthest.