The　energy-band　diagram　of　GaAs/AlGaAs　multiple　quantum　well　infrared　photodetector(QWIP)　is　calculated　by　using　Schrodinger　equation　and　Poisson　equation.　The　photoluminescence　(PL)　scan　has　been　performed　on　the　material　of　QWIP.　With　theoretical　calculation,　the　peak　response　wavelength　of　QWIP　is　determined.　The　absorption　measurement　of　the　devices　was　performed　in　a　fourier　transform　infrared　spectrometer(FTIR).　The　calculated　result　shows　that　the　theoretical　result　which　is　calculated　by　the　proposed　method　is　considerably　coherent　with　the　photocurrent　spectrum　for　the　same　sample.　The　photoluminescence(PL)　scan　provides　a　prompt　way　for　detecting　wavelength　before　process　and　it　improves　the　development　of　this　technology　effectively.