Abstract: The history and recent development of infrared detectors (IRD) are discussed; the characteristics and the existed problems of the conventional GaAs/GaAlAs quantum well infrared photodetectors (QWIP) are particularly analysed. According to a new conception of GaAs QWIPs proposed by Shen G D and the achievement gained by Du C X and Deng J, physics model is established,and numerical,simulation is conducted.The effect of the device parameters upon the device characteristics and device design are studied carefully. Moreover, The new type of GaAs/GaAlAs QWIPs with bias-tunedwavelength is presented.