A system and a method for optimizing machining force of NC program is disclosed. The system includes a tool path acquisition unit and a NC program optimizing unit; the tool path acquisition unit is for acquiring a coordinate set of points composed by a coordinate information outputted by a controller, and modifying with respect to the coordinate set of points so as to form a tool path; the NC program optimizing unit is for analyzing machining force in accordance with the tool path, a tool information, a workpiece information and a machine tool characteristic information, and modifying with modified processing feed rates to generate an optimized NC program.