Spectral matching factor is an important parameter for the performance evaluation of the low-light-level (LLL) night vision system. However, the traditional spectral matching factor can only reflect the degree of coincidence between the spectrum of the photocathode and the target in the response wavelength range, and cannot distinguish the performance of different generations of photocathode in LLL night vision system. Therefore, an evaluation factor equation was established to describe the effect of the photocathode on the detected scene, combined with the initial contrast, the integrated sensitivity and the spectral conversion coefficient. Meanwhile, the initial contrast formula of the target and the background was improved to increase the accuracy of the initial contrast. The spectral matching factors and the proposed evaluation factors of a super-second generation photocathode material and a third generation photocathode material which named New S₂₅and GaAs with different targets were calculated. The spectral matching factor between New S₂₅and the target was greater than that between GaAs and the target, which proved the limitation of the spectral matching factor. The evaluation factor between GaAs and the target was greater than that between New S₂₅and the target, which proved that the proposed evaluation factor could evaluate the performance of LLL night vision system more effectively.