One of the most challenging issues in robotic machining process is to know the vibration/chatter characteristics. To reduce the trial and error frustration, this paper presents the underline mechanism and theoretical analysis to provide physical understanding for the onset of chatter problem and principles to prevent that. First, the cutting force model and robot structure model are established for a systematic analysis of chatter mechanism. Completely different from common woes of regenerative chatter in conventional CNC machine paradigm, another type of chatter, namely, mode-coupling chatter was identified as the dominant source of vibrations in robotic machining, largely due to the inherent low structure stiffness of industrial robot. In-depth analysis for stability criteria and experimental verifications are then presented followed by the guidelines of process configuration and parameter selections to achieve chatter free machining operation.