The present disclosure illustrates a system for automatically and precisely positioning a robotic arm and method thereof. A control computing apparatus of the present disclosure controls a probe of the robotic arm to touch one of the positioning devices, and acquires a moment variation of each of the axes from a moment sensing device of the robotic arm, and then computes the distance between a geometric center of the touched positioning device and a coordinate origin according to a geometric feature of the touched positioning device, and then positions the robotic arm according to the moment variations of the axes and the distance between the geometric center of the touched positioning device and the coordinate origin. Therefore, the technical effect of quickly, precisely positioning the robotic arm without the error accumulation can be achieved.