This　paper　focused　on　the　intake　and　exhaust　structure　optimization　of　a　single-screw　expander　(SSE)　by　using　numerical　method.　The　effects　of　internal　volume　ratio,　the　shape　and　clearance　height　of　the　intake　port　and　exhaust　area　were　numerically　analyzed　(R123　and　HFO-1336mzz(Z)　were　selected　as　working　fluids)　to　reduce　the　energy　losses　(more　than　30%)　caused　by　pressure　loss　and　leakage　in　intake　process　and　exhaust　pressure　loss.　The　suggestions　of　reducing　the　internal　volume　ratio　and　clearance　height　at　intake　port　and　removing　the　closed　helix　line　were　given　based　on　the　simulation　results.　Then,　the　optimized　SSE　was　developed　and　experimentally　tested　in　ORC　system　with　R123　as　working　fluid.　Results　showed　that　the　filling　factor　of　the　prototype　was　reduced　from　125%　to　nearly　100%　and　the　highest　shaft　efficiency　was　increased　from　56%　to　67.7%　at　3000　rpm.　The　enhanced　performance　of　the　new　prototype　proves　the　correctness　of　the　numerical　optimization　and　this　is　expected　to　provide　guidance　for　the　design　of　SSE.　(C)　2020　Elsevier　Ltd.　All　rights　reserved.