We present a theoretical investigation of a staircase-like quantum well infrared photodetector (QWIP). It detects wavelength between 7.6 µm and 13.5 µm range at an applied electric field of F = 1.9x10 4 V/cm at 77 K. The dark current density was found to be around 2x10 -7 A/cm 2 at operating bias, which is lower than the conventional QWIPs in the literature. 1 Introduction Quantum-well infrared photodetectors (QWIPs) have been developed in the past ten years from the fundamental-physics point of view towards to large-area focal plane arrays [1][2][3]. In a standard QWIP, identical quantum wells are grown by successively to achieve a period. In this structure three asymmetric quantum wells are composed by one period. Thus each period contains three asymmetric staircase-like quantum wells. This provides us opportunity to perform asymmetry in each well and barrier parameters in one period. Variation from the standard QWIP structure have been recently proposed as a single wavelength bound to bound transition [4] and broadband bound to continuum transition [5] staircase-like detectors working in long-wavelength atmospheric windows. The advantage of the staircase-like structure has been shown as low dark current density (2x10 -7 A/cm 2 ) [5]. In this paper, we present a theoretical study of a broadband staircase-like infrared detector with low dark current density. Each quantum well is sensitive to detection wavelengths of 7.6 µm, 9.7 µm and 13.5 µm respectively at an applied electric field of F = 1.9x10