As　one　of　the　most　important　components　in　a　rotor-bearing　system,　journal　bearings　provide　proper　support　and　damping　to　the　rotor　so　that　it　can　run　both　smoothly　and　efficiently　and　keep　stable　under　different　working　conditions.　As　the　rotating　speed　of　the　rotor　growing　faster　and　load　getting　heavier,　the　traditional　cylinder　journal　bearing　can　no　longer　meet　the　demand　of　stabilizing　the　rotor,　so　different　kinds　of　non-　circular　journal　bearings　were　invented,　such　as　elliptical　bearing,　multi　lobe　bearing,　wave　bearing　and　etc.,　to　provide　better　stability　and　greater　load　capacity.　However,　these　kinds　of　non-　circular　bearings　were　mostly　designed　by　experience　of　the　engineers,　and　also　the　current　hydrodynamic　bearing　design　methodology　still　depends　on　empirical　design.　There　lacks　of　corresponding　theoretical　foundation.　In　order　to　develop　a　theoretical　method　for　bearing　designing,　an　innovative　analyzing　approach　needs　to　be　carried　out　to　explore　the　mechanism　of　the　bearings　and　its　performance.　In　this　paper,　a　new　approach　is　presented　focusing　on　the　profile　of　each　bearing　and　their　film　thickness.　A　universal　mathematical　expression　for　different　types　of　non　circular　bearings　has　been　put　forward　based　on　the　Fourier　series　theory.　The　influence　of　periodic　harmonics　of　film　thickness　on　the　static　performance　of　non-circular　bearings　of　finite　length　is　studied　for　incompressible　lubricant.　The　results　show　that　the　film　thickness　can　always　be　expanded　into　a　Fourier　series,　and　the　harmonic　components　of　film　pressure　can　be　obtained　by　solving　the　Reynolds　equation.　Finally,　the　relation　between　the　k-th　order　harmonic　component　H-0,H-k　and　the　corresponding　static　pressure　component　P-0,P-k　is　established.　This　new　investigation　can　be　used　to　improve　the　non-circular　bearing　designing　methodology　with　theoretical　guidance.