The dark current suppression circuit and the equivalent circuit model of the terahertz quantum-well photodetectors (QWPs)are introduced. The transport mechanisms of dark current and photocurrent are analyzed theoretically. Because the transport model of terahertz QWPs is very complex,the analytical expression for the current-voltage relations used in the circuit model of terahertz QWPs cannot be obtained precisely. By fitting the experimental dark current-voltage and photocurrent-voltage data,the effective voltage controlled current source (VCCS)circuit model of terahertz QWPs is established. The effective circuit model is used to design the dark current suppression module and the signal source in readout circuit. The numerical simulation results show that the effective circuit model of terahertz QWPs works well. Compared with the traditional dark current suppression module,the VCCS circuit model can accurately suppress the dark current when the voltage of the terahertz QWPs changes. It’s more suitable for the dark current suppression module of the terahertz QWPs in the readout circuit.