This study presents the evaluation of the machining stabilities of a milling machine tool. For this purpose, we first conducted the vibration tests on the spindle tool to assess the tool tip frequency response functions along the principal modal axis. And then, basing on the orientation dependent stability analysis model proposed in this study, we evaluated the variation of the dynamic characteristics of the spindle tool and the corresponding machining stabilities at a specific feeding direction. Following the stability analysis model, the limited axial cutting depths for stable machining within the whole interested feeding directions were obtained. Current results demonstrate that the stability boundaries and limited axial cutting depth of a specific cutter were affected to vary with the changing of the feeding direction and the feeding height of spindle head. There critical axial depth can be increased by 21% when the spindle head was moved from lower to a higher position. The predicted stability boundary also suggests the desired machining condition to avoid the occurrence of the chattering during the countering machining. This also indicates the strength or weakness of the structure characteristics of the spindle tool system, giving the ways for improving the machining performance or dynamic characteristics of the machine tool.