The　eddy-current　method　has　been　employed　to　realize　the　real-time　measurement　of　thickness　distribution　and　polishing　endpoint　detection　of　metal　films　during　the　metal　chemical　mechanical　polishing　(CMP)　process.　However,　accuracy　and　sensitivity　in　thickness　measurement　can　be　significantly　impacted　by　a　variation　in　lift-off　distance　(about　3.5　mm),　attributable　to　the　progressive　wear　of　the　polishing　pad.　This　paper　proposes　a　novel　triple-coil　sensor　system,　integrated　with　an　alternating-current　bridge　and　designed　for　high-precision　metal　film　thickness　measurement.　Subsequently,　the　measurement　performance　of　the　bridge　output　voltage　was　scrutinized　using　a　theoretical　model　and　a　trans-dimensional　finite　element　analysis　model　of　electromagnetic　fields　and　circuit　coupling.　The　correlations　between　the　amplitude,　phase,　and　the　ratio　of　the　real　part　to　the　imaginary　part　of　the　output　voltage,　in　context　with　film　thickness,　were　determined　at　assorted　excitation　frequencies　and　lift-off　distances.　Both　theoretical　equations　and　simulation　results　affirmed　that　the　phase　and　ratio　were　more　resistant　to　lift-off　distance　variations　than　the　amplitude,　and　a　linear　relationship　was　identified　between　the　ratio　and　film　thickness.　Furthermore,　the　thickness　measurement　performance　of　the　amplitude　and　phase,　when　the　triple-coil　was　imbalanced,　was　dissected　via　numerical　simulation.　A　profound　understanding　of　the　proposed　system　was　provided　and　beneficial　for　the　practical　applications　in　real-time　thickness　measurements　of　metal　films　during　the　metal　CMP　process.