In order to determine the relatoinship between the Al content and the peak wavelength of quantum well infrared photodetector (QWIP).and establish another one between charact erization of microstructure and macroscopic properties of samples.The author designed two device-samples with different Al content based on the bound to the quasi bound state transitions (b-qbQWIP) modle.Corresponding tests h ave been done,including photoresponse spectra,photoluminescence spectra and hig h resolution transmission electron microscopy (HRTEM).The relation between Al conte nt and the peak wavelength is analyzed and discussed in theory.Two sample-devices of GaAs/AlxGa 1－xAs quantum well infrared photodetec tors have been made by using metal organic chemical vapor deposition (MOCVD).Al content of 1# sample is 0.23while that of 2# one is 0.32.The photoresponse spectra are obtained at 77K by using Fou rier transform spectrometer while photolumi nescence spectra are tested at room temperature for two sample-devices of GaAs/AlxGa1－xAs quantum well infrared ph otodetectors.The peak wavelengths of 1# and 2# are 8.36μm and 7.58μm from photoresponse spectra,wh ile the ones are 9.672μm and 7.928μm according to Schrodinger equation.The main reason for 1# error much larger is crystal lattice mismatch between GaAs and AlGaAs and not precise controlling dur ing growth of quantum well material after the crystal structure is investigated by using high-resolutio n transmission electron microscope (HRTEM).It shows that reducing Al content will lead to subband narrowed and peak wavelength red-shift .Photoluminescence results are consistent with Schrodinger equation.