Noise equivalent temperature difference (NETD) is a key indicator for evaluating the sensitivity of infrared detectors. By changing the readout circuit structure and improving the charge processing capability of the readout circuit, the NETD value of the detector is increased from 10 mK to below 1 mK. When the noise is less than 1 gray level, the NETD value obtained by the existing test method is low, resulting in an overestimation of the recognition distance when the whole machine is used, which is inconsistent with the actual results. The optimization method proposed in this article makes the test results more consistent with the system application indicators. After analysis, it is believed that the detector used is more suitable for low-speed targets or relatively static scenes; compared with conventional detectors, the recognition distance of this detector is more affected by the same optical temperature change. Users are advised to pay attention to the impact of optical temperature stability.