Asymmetric flexible machining system has been widely used in numerical control machining. In traditional milling dynamics model, the cutter feed direction is usually defined as parallel to its vibration DOF, while the nonparallel condition and its induced milling dynamics response are not deeply considered. This paper presents a general dynamics modeling method for asymmetric flexible machining systems. First, to the best of the author’s knowledge, a new dimension named feed direction is proposed, which is used to establish the generalized coupling relationship between the vibration displacement and the regenerative milling force, thus improve the applicability of the milling dynamics model and reduce the experimental workload compared with the traditional modeling. Second, through the theoretical and experimental research, it is shown that the asymmetric flexible machining system has a significant feed direction-dependent characteristics, and implied the existence of high performance machining region with higher stability and lower surface location error (SLE) by contrast with the symmetric milling system and the traditional models. Finally, by controlling the feed direction angle, the milling parameters in roughing and finishing operations are optimized, and the machining efficiency has been greatly improved on the premise of stable cutting and machining accuracy.