The invention relates to a medical external bone fixer which is particularly provided with a long needle stand, a short needle stand and a connecting set. The connecting set is combined with the long needle stand in a linear deformation manner; the short needle stand is conveniently fixed on the long needle stand in a rotary and tight manner or in a reverse and loose manner. A rotatable componentof the long needle stand is screwed at the screw axis end of a ball-head screw of the connecting set through a screwed hole of the rotatable component, so as to push a ball-head screw axis to extend or withdraw relatively to the long needle stand; a plane is arranged on the screw axis end along the long axis direction in a tangent manner; a threaded bolt is screwed into the long needle stand and butts against the plane of the screw axis end to lead the ball-head screw axis to be fixed relatively to the long needle stand; another cambered surface tightening rod of the connecting set acts on the combination between another ball-head end of the ball-head screw and the short needle stand in a rotary and tight manner or in a reverse and loose manner.