The　thermodynamic　efficiency　of　Organic　Rankine　Cycle　(ORC)　obtained　from　experimental　systems　has　been　obviously　lower　than　theoretical　results.　One　of　the　reasons　is　that　some　elements　affecting　the　efficiency,　such　as　pressure　losses　in　evaporator,　condenser　and　pipes,　have　not　been　deeply　discussed　and　optimized.　The　present　manuscript　detailed　and　examined　the　influences　of　pressure　losses　on　ORC　thermodynamic　efficiency.　Pressure　losses　in　ORC　system　were　divided　into　three　categories:　High　Pressure　Loss　of　the　first　category　(HPL1),　High　Pressure　Loss　of　the　second　category　(HPL2)　and　Low　Pressure　Loss　(LPL).　A　formula　was　developed　to　describe　the　relationships　between　three　categories　of　pressure　losses　and　ORC　thermodynamic　efficiency.　Through　analyses　of　the　formula,　it　is　found　that　the　adverse　impacts　of　pressure　losses　on　thermodynamic　efficiency　are　very　different,　mainly　depending　on　the　characteristic　specific　volume　of　working　fluid　in　certain　state.　Because　the　very　different　specific　volume,　under　a　same　value　of　pressure　loss,　LPL　mostly　leads　to　the　largest　thermodynamic　efficiency　drop　of　ORC　system,　HPL1　does　less　and　HPL2　does　the　least.　The　influences　of　LPL　are　normally　3-21　times　larger　than　that　of　HPL1,　and　30-50　times　larger　than　that　of　HPL2.　The　conclusions　will　serve　as　a　guide　for　engineering　applications　of　ORC　system.