The invention discloses a flexible multi-joint surgical instrument for robot assisted minimally invasive surgery, and relates to the technical field of enterocoelia minimally invasive surgery department medical facilities. The instrument can achieve spatial displacement and positioning of tail end operating forceps by itself inside a patient, the tail end gesture adjusting capability of the surgical instrument is enhanced, the good flexibility is achieved, and the tissue surgical operation is completed inside the small space; by means of a self-rotation joint designed between the wrist of the surgical instrument and the tail end operating forceps, and the problem that joint restoration is needed during autorotation is avoided; the instrument comprises the tail end operating forceps mechanism, the autorotation joint, the wrist flexible joint and a power driving box; the power driving box comprises a wiring pipe, a shell, an upper base plate, a lower base plate, five sets of motor rope sheave devices, a rope guiding wheel set and a rope guiding column set; one end of the wiring pipe is connected with the tail end ball hinge structure of the wrist flexible joint, and the other end of the wiring pipe is fixed to the lower base plate. The instrument is used for the robot assisted minimally invasive surgery.