Abstract: W-band Low-noise amplifiers (LNAs) are key front-end components in millimeter-wave radiometers, radar, and communication receiver systems, and their noise performance directly determines the system sensitivity and dynamic range.To address the limited availability of domestic millimeter-wave LNAs characterized under cryogenic operating conditions, this work establishes a cryogenic performance measurement platform covering 30~300K and performs low-temperature characterization of domestically manufactured millimeter-wave LNA samples originally designed for room-temperature operation. Experimental results demonstrate pronounced performance enhancement at cryogenic temperatures: as the temperature decreases from 300 K to 80 K, the gain increases by approximately 3 dB and the noise temperature is reduced by about 170 K. By incorporating an error-cascade model and applying waveguide attenuation corrections, the optimal operating temperature of the domestic millimeter-wave LNA is identified to be approximately 80 K. This study provides practical experimental evidence and parameter references to support the deployment of domestically developed W-band LNAs in millimeter- and sub-millimeter-wave radiometer systems.