<p>Accurate on-site monitoring of the humidity in the flue gas from coal combustion is crucial for ensuring the accuracy of particulate matter (PM) measurements and improving the energy efficiency of power generation systems. However, developing humidity sensors with both high sensitivity and high selectivity remains a significant challenge, mainly due to the harsh working environment in the flue (high temperature and corrosiveness) and the significant cross-sensitivity caused by the similar electrolysis voltages of H₂O and CO₂. To address this issue, a series of amperometric sensors based on yttria-stabilized zirconia (YSZ) were fabricated, which employed La_1−xSr_xFeO₃ (x = 0.2, 0.4, 0.6, 0.8) perovskite sensing electrodes, and the influence of Sr²⁺ doping on the humidity sensing performance was systematically studied. The results showed that the lightly doped La_0.8Sr_0.2FeO₃ electrode exhibited the best performance, with a sensitivity of up to 70.4 µA/vol%, and could also effectively resist carbon dioxide interference. Moreover, the sensor demonstrated excellent repeatability and long-term stability in high-temperature and high-humidity environments. This research provides a promising material design and sensing strategy for on-site humidity monitoring in complex industrial flue gas environments.</p>