Existing　bearing　fault　diagnosis　approaches　utilize　signal　processing　techniques　in　combination　with　vibration　measurements.　The　common　vibration　measurement　method,　using　accelerometer,　has　disadvantages　such　as　position-constrains,　high　costs　and　external　interferences.　Meanwhile,　the　commonly　used　modelling　methods　of　motor　are　not　able　to　analyse　both　mechanic　and　electromagnetism　simultaneously.　For　detecting　the　fault-related　frequencies　in　motor　current,　a　mathematical　model　is　developed　in　this　paper　based　on　modified　winding　function　approach　(MWFA).　The　simulation　results　show　that　the　fault-related　characteristic　frequencies　can　be　exactly　found　in　the　spectrum　results　of　motor　current.　The　proposed　method　is　proven　to　be　feasible.　©　2020　Institute　of　Physics　Publishing.　All　rights　reserved.