The essential factors of enhancing the detecting limitation of low-light imaging system are enough accumulation time to the light signal. After the principle is demonstrated for the accumulation time of CCD to low temperature, it shows the localization and complexity. So, we put forward a device for promoting the low-light level imaging system' detection limit in which a magnetic mirror structure is coupled between the photocathode and the photoelectron acceptor (screen target), viz. this is the method of microchannel electron vase plate. It can be used in the small-scale integration imaging system respectively to enhance the detection limit of low-light level by the new way. The new photoelectron acceptor can assure the image signal's accumulation time. By this new way, the signal-to-noise of imaging system can be improved and detection limit of low-light imaging system is expanded. The physics principle of the field of magnetic mirror is demonstrated and the simulation values showed the expected result sensitive detection limit 10-11 lx can be realized at the room temperature instead low temperature.