Using one band effective mass approximation and shooting method, optimized parameters of quantum well infrared photodetector structure were calculated. Taking into account high order effect of band nonparabolicity, the device structure with a peak detection wavelength of 8 μm were designed. Based on the calculated result, GaAs/AlGaAs multiwell material was grown. Then single-element QWIP device were fabricated and characterized. Symmetrical I-V curves showed very good quality of the material and successful process in device fabrication. Spectral responsivity exhibited peak wavelength of 7.96 and 7.98 μm, which were in excellent agreement with our designed value.