This　paper　fully　describes　the　working　principle　of　slide　valves　in　single-screw　expanders　(SSEs).　A　geometric　analysis　of　suction　and　volume　ratio　slide　valves　is　presented　to　determine　the　relations　between　volume　ratio,　suction　closure　volume,　discharge　opening　volume　and　slide　valves　displacement.　An　organic　Rankine　cycle　(ORC)　thermodynamic　model　with　SSE　integrated　with　slide　valves　is　developed　to　analyze　the　power　output　of　SSE　and　the　net　power　output　of　ORC　system　and　variation　law　of　slide　valves　displacement.　Analysis　of　a　typical　ORC　system　under　changing　operating　conditions　shows　that　the　power　output　of　the　expander　and　the　net　output　power　of　the　ORC　system　with　slide　valves　are　much　better　than　those　without　slide　valves.　When　the　condensing　temperature　is　40　degrees　C　and　the　waste　availability　is　80　kW,　the　increase　in　output　power　and　net　output　power　are　approximately　3.4　kW　and　5　kW,　respectively.　The　presented　geometric　analysis　of　slide　valves　and　the　thermodynamic　model　integrated　with　slide　valves　can　be　used　to　provide　a　theoretical　and　technical　basis　for　designing　the　slide　valves　of　SSEs　and　the　control　strategies　of　slide　valves　under　varied　operating　conditions.