We present a novel structure of multi-quantum well infrared photodetector(QWIP).In the new structure device,a p-type contact layer replaced the n-type layer and on the top of the conventional structure of QWIP,and a small tunneling current replaced the large compensatory current,which made the device with low dark current and low noise characteristics.The experimental result of dark current accorded with the calculated result,and the noise of the new structure QWIP decreased to one third of the conventional QWIP.