Abstract: The general performance evaluation theory of low light level (LLL) night vision system is studied based on signal detection and human vision. Simultaneously, the minimum resolvable contrast (MRC) model is deduced. Combining the optical transfer properties with the signal-to -noise ratio of system, the mathematical relationship among target characteristic, LLL night vision system and human visual system is established. The simulation result shows that the relative error of the limited sensitivity calculated by MRC model is 3.08 %, compared with the reality of system. The MRC model mentioned in the paper is a more perfect one for evaluating the performance of LLL night vison system.