Miniaturized components are increasingly in demand for various industries. Micro milling operations can fabricate miniaturized components with high relative accuracy. In micro milling process, the analysis of cutting force plays an important role in characterizing the machining process, as the tool wear and surface texture depending on the cutting force. In this paper, the orthogonal experiments under slot-milling and side-milling with typical micro three dimensional parts are done by the developed three-axis micro milling machine tool, and the micro milling force is measured and analyzed. In order to improve the processing efficiency and processing accuracy of micro milling process, the impact law of the spindle speed, axial cutting depth, feed per tooth and other parameters on cutting force is deeply studied, and the machining parameters is also optimized.