Abstract: In this study, a commercially available macroporous adsorption resin was used as the support, and tetraethylenepentaamine (TEPA) as the amine source. An ultrasonic-assisted wet impregnation method was employed to prepare an amine-functionalized solid-state amine adsorbent for the direct capture of low-concentration CO2 from ambient air. The material structure was systematically analyzed using a series of characterization techniques, and its adsorption performance, operational adaptability, and cycle stability were evaluated in a fixed-bed reactor. The results indicate that HP D100 resin, with its large pore volume and high proportion of macropores, enables efficient loading and uniform dispersion of TEPA; a 30% TEPA loading was determined to be the optimal ratio, with an adsorption capacity of 1.81 mmol/g under drying conditions at 40 °C; humidity significantly enhances adsorption performance, reaching 2.55 mmol/g at 80% relative humidity, and moisture effectively counteracts the oxidative inhibition caused by oxygen. After 10 cycles, the adsorption capacity retention rate exceeded 86%, indicating good cycle stability. The adsorbent maintained stable adsorption capacity in a simulated real-world atmospheric environment containing both oxygen and water, although cycle stability showed some decline. This resin-based adsorbent requires no granulation, is simple to prepare, and has controllable costs, demonstrating good application potential in the field of direct air CO2 capture.