We perform a theoretical study on a low dark current InGaAs/GaAs very-long-wavelength (＞12 μm) quantum well infrared photodetector (VLW-QWIP), based on a double barrier resonant tunnelling structure (DBRTS). The ground tunnelling state of the central quantum well (QW) of the DBRTS can resonate with the first excited bound state of the doped InGaAs QW by adjusting the structure parameters of the DBRTS. Investigation of the carrier transport performance of this device is carried out based on quantum wave transport theory. It has been shown that the dark current in this device can be significantly reduced by two orders compared to conventional InGaAs/GaAs VLW-QWIPs, while the photocurrent is almost the same as those in conventional VLW-QWIPs. This DBRTS integrated VLW-QWIP structure may stimulate the experimental investigation for VLW-QWIPs at high operation temperatures.