Terahertz (THz) quantum well photodetectors (QWPs) are an extension of quantum well infrared photodetectors in the THz region.We construct an imaging system based on a THz QWP with a narrow response range from 3 THz to 6 THz.The peak responsivity of the THz QWP having background-limited performance is about 0.S A/W,and the corresponding detectivity reaches 1011cm.Hz1/2/W at temperature of 4.2K.We obtain the images of a concealed object by the imaging system and prove that THz QWPs have the potential for imaging applications.