Brightness gain is an important parameter of low-light image intensifiers. It affects the accuracy of the object-background contrast in low-light night vision environments. Based on the principle of contrast tests, this study analyzes the relationship between the brightness gain and the object-background contrast, as well as influencing factors, via the object-background contrast test on an ICCD with different brightness gains. The results show that when the brightness gain is 12000, 8300, or 6000 cd/(m2·lx) and the ambient illuminance iswithin the range of[2×10-3, 8×10-3] (lx), the object-background contrast is minimally affected by thebrightness gain. However, when the illuminance is outside this range, the object-background contrast test result may be distorted due to the influence of the brightness gain. The results of this study can guide the improvement of accuracy of ICCD object-background contrast tests.