For　this　study,　a　test　rig　of　free　piston　expander-linear　generator　(FPE-LG)　for　organic　Rankine　cycle　(ORC)　waste　heat　recovery　system　is　built.　Based　on　the　free　piston　expander-linear　generator　test　rig,　an　experiment　of　external　load　resistance　effect　on　the　motion　characteristics,　indicated　efficiency,　output　performance　and　energy　conversion　efficiency　of　the　free　piston　expander-linear　generator　is　conducted.　The　displacement　and　velocity　of　the　free　piston　assembly　increase　with　the　external　load　resistance.　The　indicated　efficiency　of　the　free　piston　expander　(left　cylinder)　decreases　with　the　external　load　resistance.　As　the　external　load　resistance　and　intake　pressure　increase,　the　peak　voltage　output　of　the　free　piston　expander-linear　generator　increases.　The　maximum　peak　voltage　output　is　44.4　V　when　the　intake　pressure　is　3.0　bar,　the　operating　frequency　is　1.5　Hz　and　the　external　load　resistance　is　40　Omega.　The　peak　power　output　of　the　free　piston　expander-linear　generator　initially　shows　a　non-linear　relation　increase　with　external　load　resistance　and　tends　to　stabilize　in　the　end.　When　the　intake　pressure　is　3.0　bar,　the　operating　frequency　is　1.5　Hz　and　the　external　load　resistance　is　30　Omega,　the　maximum　peak　power　output　of　110　W　can　be　achieved.　The　energy　conversion　efficiency　of　the　free　piston　expander-linear　generator　increases　gradually　with　growing　of　the　intake　pressure　and　external　load　resistance　until　the　energy　conversion　efficiency　reaches　the　maximal　value,　and　then　the　energy　conversion　efficiency　decreases　with　the　intake　pressure　and　external　load　resistance.　The　maximum　energy　conversion　efficiency　can　reach　up　to　73.33%.