To improve turning process, a testing system for dynamic cutting force was established. The paper studied the dynamic cutting force theoretically and experimentally with the frequency domain analysis. Cutting experiments were conducted for new tools, worn tools, and broken tools respectively. And a comparison among three forces’ power spectrum was made. The results show that the power spectrum value of radial force in the frequency range of 2450~3100 Hz has a close relation to the state of tool wear and tool breakage, which can be used to monitor the cutting process in real time.