Journal　bearing　is　one　of　the　most　important　components　for　supporting　high　speed　rotating　machinery　such　as　compressors　and　turbo　machines.　In　recent　trends,　non-circular　journal　bearings　(lemon　bearing,　three-lobe　bearing,　four-lobe　bearing,　etc.),　for　their　greater　load　capacity　and　better　stability,　have　become　a　superior　choice　and　found　wide　spread　application.　In　this　paper,　the　nonlinear　oil　film　force　is　expressed　using　the　dynamic　stiffness　and　damping　of　1st-3rd　order.　And　the　film　thickness　and　pressure　are　analyzed　using　Fourier　method,　so　that　the　corresponding　harmonic　components　and　their　deeper　connection　can　be　further　explored.　The　paper　shows　that　the　nonlinear　dynamic　performances　are　connected　closely　with　the　bearings＇　profile,　and　lays　the　foundation　for　expressing　the　precise　nonlinear　oil　film　force.