In　this　paper,　a　mathematical　model　of　fin-and-tube　evaporator　of　ORC　system　used　for　waste　heat　recovery　of　a　diesel　engine　is　established.　Particle　swarm　optimization　(PSO)　algorithm　is　applied　for　the　multi-objective　optimization　of　the　fin-and-tube　evaporator.　Key　geometrical　parameters　such　as　the　inlet　radius　of　the　tube　side,　the　inlet　radius　of　the　shell　side,　fin　height,　fin　thickness　and　fin　spacing　are　selected　as　decision　variables.　Total　annual　cost,　volume　of　tube　bundle,　and　exhaust　pressure　drop　are　considered　as　optimization　objectives　(objective　functions).　The　linear　weighted　method　is　used　to　assign　a　weight　coefficient　to　each　objective　function.　Calculation　results　obtained　by　MATLAB　R2010a　clearly　show　a　contradictory　relationship　among　the　objective　functions.　For　a　specific　operating　condition　of　the　diesel　engine,　multi-objective　optimization　of　the　fin-and-tube　evaporator　is　performed,　and　the　optimal　design　is　obtained.　Compared　with　the　results　of　the　original　design,　the　multi-objective　optimization　results　are　more　satisfactory,　the　volume　of　tube　bundle　is　increased　by　6.49%,　meanwhile　the　total　annual　cost　is　decreased　by　71.46%　and　exhaust　pressure　drop　is　reduced　by　27.6%.　The　PSO　algorithm　based　fin-and-tube　evaporator　design　method　is　beneficial　to　improving　the　performance　of　the　diesel　engine-organic　Rankine　cycle　(ORC)　combined　system.