This　paper　proposes　a　hybrid　WAAM　(wire　arc　additive　manufacturing)　and　milling　process　(HWMP),　and　highlights　its　application　in　the　fabrication　of　stiffened　panels　that　have　wide　applications　in　aviation,　aerospace,　and　automotive　industries,　etc.　due　to　their　light　weight　and　strong　load-bearing　capability.　In　contrast　to　existing　joining　or　machining　methods,　HWMP　only　deposits　stiffeners　layer-by-layer　onto　an　existing　thin　plate,　followed　by　minor　milling　of　the　irregular　surfaces,　which　provides　the　possibility　to　significantly　improve　material　utilization　and　efficiency　without　any　loss　of　surface　quality.　In　this　paper,　the　key　performances　of　HWMP　in　terms　of　surface　quality,　material　utilization　and　efficiency　are　evaluated　systematically,　which　are　the　results　of　the　comprehensive　effects　of　the　deposition　parameters　(e.g.,　travel　speed,　wire-feed　rate)　and　the　milling　parameters　(e.g.,　spindle　speed,　tool-feed　rate).　In　order　to　maximize　its　performances,　the　optimization　is　also　performed　to　find　the　best　combination　of　the　deposition　and　the　milling　parameters.　The　case　study　shows　that　HWMP　with　the　optimal　process　parameters　improves　the　material　utilization　by　57%　and　the　efficiency　by　32%　compared　against　the　traditional　machining　method.　Thus,　HWMP　is　believed　to　be　a　more　environmental　friendly　and　sustainable　method　for　the　fabrication　of　stiffened　panels　or　other　similar　structures.