A comprehensive analysis on the relationship between the barrier height and the peak wavelength of bound-to-quasi-continuum Quantum Well Infrared Photodetector(QWIP) was demonstrated, together with its effect on characterization of microstructure and macroscopic optic properties of the device-sample. The GaAs/Al_xGa_1-xAs infrared quantum well material was produced via the method of Metal Organic Chemical Vapor Deposition(MOVCD). Two sample devices with different Al content(0.23 and 0.32) was designed respectively and their corresponding spectral responses were measured via Fourier Transform Spectrometer at the temperature of 77 K. The experimental results shown that sample 1# and 2# are with the peak wavelengths of 8.36 μm and 7.58 μm, which present obvious difference to the theoretical results based on Schrodinger equation (9.672 μm and 7.928 μm, corresponding to errors of 15.6% and 4.6%, respectively). By analyzing the effect of Al atoms diffusion length, it is found that the decrease of Al content is the key effect which leads to sub-band narrow down and peak wavelength red shift. Meanwhile, by using the method of High Resolution Transmission Electron Microscopy(HRTEM), it is found that the strong error of sample 1# is mainly due to the crystal lattice mismatch between GaAs and AlGaAs, together with the unsatisfied precise control during the growth of quantum well material. Above analysis demonstrates that adjusting the Al content of barrier height is an effective method to turn the peak wavelength of QWIP.