In　this　paper,　a　test　rig　of　free　piston　expander-linear　generator　(FPE-LG)　for　organic　Rankine　cycle　(ORC)　waste　heat　recovery　system　using　compressed　air　is　established.　Based　on　the　FPE-LG　test　rig,　the　experiments　of　external　load　resistance　effect　on　the　motion　characteristics,　output　performance　and　energy　conversion　efficiency　of　the　FPE-LG　are　conducted.　The　results　show　that　the　displacement　and　velocity　of　the　free　piston　assembly　increase　with　the　external　load　resistance.　As　the　external　load　resistance　and　intake　pressure　increase,　the　peak　voltage　output　of　the　FPE-LG　increases.　The　maximum　peak　voltage　output　is　44.4　V.　The　peak　power　output　initially　shows　a　non-linear　increasing　trend　when　growing　the　external　load　resistance　and　stabilizes　in　the　end,　the　maximum　peak　power　output　of　110　W　can　be　achieved.　In　addition,　the　energy　conversion　efficiency　of　the　FPE-LG　first　increases　and　then　decreases　with　intake　pressure　and　external　load　resistance.　The　maximum　energy　conversion　efficiency　can　reach　up　to　73.33%.　©　2020,　Solar　Energy　Periodical　Office　Co.,　Ltd.　All　right　reserved.