Intelligent CNC machine tool is production terminal equipment of smart factory in the era of Industries 4.0. Technical implementation of network, intelligence and collaborative manufacturing of this machine tool can not do without open smart CNC which has high stability and precision retaining ability. In this paper, aimed at real-time optimization of cutting parameters during milling process, functional software modular is designed and developed in the platform of open modular architecture CNC. The algorithm of intelligent control is integrated into system coordinator modular of CNC, which could adjust spindle speed and feed rate in real-time through processing cutting force signals. The effectiveness of proposed smart CNC is validated by thin-wall cutting experiments.