Abstract: Humidity monitoring is essential in numerous fields, including precision manufacturing, semiconductor packaging, lithium battery storage, and human health monitoring. However, most existing room-temperature humidity sensors still face challenges such as high cost, narrow detection range, limited anti-interference capability, or slow response and recovery times, hindering their suitability for emerging Internet of Things and flexible electronics applications. To address this, we grafted diphenylamine units onto the perylene diimide (PDI) molecular platform and applied protonation regulation using hydrochloric acid. Through π-π stacking interactions with single-walled carbon nanotubes (SWCNTs), a one-dimensional van der Waals heterostructure was formed in situ at the interface, enabling the fabrication of a chemiresistive humidity sensor. This device exhibits rapid, reversible response across a wide relative humidity (RH) range of 10%-90%, with a theoretical detection limit as low as 0.28%. At 90% RH, the response time is only 1.68 seconds, and the recovery time is on the order of seconds, significantly outperforming most commercial humidity sensors. Moreover, the sensor demonstrates excellent selectivity toward water molecules, showing negligible responses to ammonia (NH3), carbon dioxide (CO₂), hydrogen sulfide (H₂S), carbon monoxide (CO), and various volatile organic compounds, confirming strong anti-interference capability. Mechanistic studies reveal that the protonated diphenylamine side chains enhance interfacial polarity, which cooperates with the carbonyl oxygen sites of the PDI backbone to enable efficient water molecule capture and charge transfer, thereby substantially improving sensing performance. The material design and device fabrication strategy presented herein provide valuable theoretical and technical foundations for developing low-power, integrable, high-performance humidity sensing systems for large-scale applications in IoT environmental monitoring, intelligent packaging, and breath analysis.