Abstract: The reduced trend of operable pixel factor of medium wave or long wave infrared focal plane array must be resulted from some failure mechanism caused by manufacturing process defects, specific working stress or environmental stress. Mathematical model based on the output signal voltage of infrared detector, through the analysis of signal transmission and the statistical analysis of performance evaluation test data, visualization means such as statistical graphs, response curves and output signal voltage grayscale were used to visually express non-effective pixel characteristics, such as the types, number, locations, distribution, and output signal voltage, noise voltage, response voltage. Statistical analysis shows that the average apparent operable pixel factor is reduced by 1.07 percentage points relative to the initial operable pixel factor during use of the medium wave 320×250 detector Dewar cooler assembly of pixel pitch 15 μm, 86.45% of apparent non-effective pixels are unstable flickering pixels and drifting pixels on average. Design and manufacturing defects cause the response line of non-effective pixels to be horizontal, and the response voltage tends to 0. The thermal adaptation stress is the reason for non-effective pixel clusters of linear. A method was proposed to screen and identify non-effective pixels based on the criterion that the pixel signal voltage exceeded the average value of ±(6%~7.5%) under different blackbody temperatures.