In　the　mobile　industrial　human　machine　interaction　(HMI)　based　on　wireless　sensor　networks,　the　engineer　has　to　manually　select　the　target　machine　from　a　long　list　which　may　lead　to　wrong　connection　and　waste　of　time.　We　observe　that　the　engineer　should　face　to　the　machine　during　the　interaction　to　ensure　that　the　machine　works　accurately,　and　this　characteristic　makes　the　proximity　estimation　algorithm　suitable　to　simplify　the　data　connection.　However,　due　to　the　densely　deployed　machines　and　the　frequent　HMI　in　the　industrial　plant,　the　existing　algorithms　can　not　provide　sufficient　accuracy　with　limited　latency.　In　this　paper,　we　implement　a　mobile　industrial　HMI　testbed　to　evaluate　the　characteristics　of　wireless　communication　in　the　face-to-machine　HMI,　and　then　propose　the　face-to-machine　proximity　estimation　(FaceME)　algorithm　based　on　the　analytical　results.　The　experimental　results　prove　that　FaceME　can　provide　guaranteed　estimation　accuracy　and　low　time　complexity　that　satisfies　the　requirements　of　the　face-to-machine　HMI.