Abstract: The authors introduce the theorectical modeling method and the stability experiment method of milling process. Through the theoretical model and milling experiment they discuss the condition of producing forced vibration and chatter in milling process and the chatter characteristics. The theoretical study and experimental analysis show that the forced vibration becomes stronger with the increase of milling speed while chatter presents a certain periodicity with the speed change; The vibration energy in the stable milling process mainly concentrates in the passage rate of cutter tooth and its whole number times, but when milling chatter takes place, it concentrates near the low order natural frequency of the system.