Two-stage　ORC　(Organic　Rankine　Cycle)　is　a　very　competitive　configuration.　However,　most　of　the　works　have　narrowed　the　studies　within　a　single　or　just　several　fluids　in　spite　of　the　great　effect　of　working　fluids　on　system　performance.　In　this　paper,　400　combinations　of　working　fluids　are　investigated.　The　evaporation　and　condensation　pressures　of　both　the　high　and　low　temperature　ORCs　are　optimized　by　PSO　(Particle　Swarm　Optimization)　with　the　objective　function　of　maximum　exergy　efficiency.　The　results　show　that　the　effect　of　fluid1　on　the　system　exergy　efficiency　is　much　greater　than　that　of　fluid2.　Critical　temperature　is　a　key　indicator　for　fluid1　selection　and　triple　point　temperature　is　a　crucial　indicator　for　fluid2　selection.　The　largest　exergy　destruction　occurs　in　the　condenser　of　cycle　II.　The　proper　solution　to　reduce　this　exergy　destruction　is　raising　the　inlet　temperature　of　LNG,　rather　than　lowering　the　condensation　temperature　of　cycle　II.