A　new　method　for　retardation　measurement　of　a　quarter-wave　plate　was　proposed.　It　was　realized　by　calculating　the　long　and　short　axes＇　values　of　the　output　elliptical　polarized　light　based　on　computer　simulations.　The　optical　measuring　system　was　simply　composed　of　a　laser,　a　polarizer,　the　quarter-wave　plate　to　be　measured,　an　analyzer　and　an　optical　detector.　The　real　retardation　can　be　obtained　by　a　data　processing　with　Mathcad.　The　principle　of　this　new　method　was　theoretically　analyzed　and　an　application　example　and　its　error　analysis　were　demonstrated　in　this　paper.　The　experiment　results　show　that　the　absolute　error　is　less　than　0.26°.　Therefore　the　main　advantages　of　the　method　are　a　few　optical　devices　required,　very　easy　to　run　and　a　big　improvement　in　measuring　accuracy.　©　2016,　Editorial　Board　of　Journal　of　Infrared　and　Laser　Engineering.　All　right　reserved.