A　new　free　piston　expander-linear　generator　(FPE-LG)　prototype　for　small-scale　organic　Rankine　cycle　(ORC)　waste　heat　recovery　system　was　developed,　and　a　new　valve　train　was　designed　to　control　the　intake　and　exhaust　process　of　working　fluid.　The　motion　characteristics,　output　performance　and　indicated　efficiency　of　the　FPE-LG　were　investigated　based　on　a　compressed　air　test　rig.　The　results　show　that　the　intake　duration　and　exhaust　duration　have　a　great　influence　on　the　motion　characteristics　and　output　performance　of　the　FPE-LG.　The　stroke　and　velocity　of　free　piston　assembly　increase　with　the　increase　of　the　intake　duration,　and　decrease　with　the　decrease　of　the　exhaust　duration.　the　valve　timing　optimization　can　significantly　improve　the　output　power　of　linear　generator.　The　maximum　value　of　voltage　is　13　V　and　the　maximum　value　of　peak　power　is　18.6　W　when　the　intake　angle　is　60°and　the　exhaust　angle　is　180°,　and　the　intake　pressure,　operating　frequency　and　the　external　load　resistance　are　1.9×105Pa,　2　Hz　and　9　Ω,　respectively.　The　velocity　and　stroke　of　the　free　piston　assembly　show　an　increasing　tendency,　and　higher　peak　voltage　and　power　output,　when　the　external　load　resistance　increases.　The　indicated　efficiency　shows　a　downward　tendency　when　the　external　load　resistance　increases.　The　indicated　efficiency　is　66.2%　when　the　external　load　resistance,　operating　frequency　and　the　intake　pressure　are　3　Ω,　3　Hz　and　1.　9×105Pa,　respectively.　©　2019,　Editorial　Department,　Journal　of　South　China　University　of　Technology.　All　right　reserved.