Abstract: High thermal efficiency is often required in the conventional unglazed solar air collectors (USAC) under crosswind conditions. The heat transfer can depend mainly on the specific heat capacity and flow velocity of the air in the flat-plate solar air collectors with the covers. In this study, a novel USAC with an air-curtain jet was proposed to enhance the thermal performance of the collector, in order to resist the crosswind interference. A combination of numerical simulation and experiment was adopted to verify the USAS performance. Initially, SolidWorks and FLUENT were used to conduct the numerical simulations. The reasonable range of the slot widths was determined for the air-curtain jet structure. Subsequently, an experimental platform was constructed, consisting of a porous aluminum plate, slotted rectangular air ducts, and insulation boards. The experiment was set in a controlled laboratory environment at Yanshan University, Hebei Province, China. A TRM-PD1 solar simulator was provided with a stable radiation intensity of 700 W/m². A hot-wire anemometer was used to monitor the outlet flow rate of 0.018 kg/s. An Agilent DAQ970 was used to record the temperature data at 20 measurement points on the collector plate surface at 10-second intervals. A series of experiments was conducted every day, in order to further reduce the influence of the environmental temperature. The experimental period lasted for one month. The results show that the air-curtain jet significantly improved the thermal performance of the collector. When the air-curtain jet was applied, the initial temperature of the inlet air increased in the pre-heated air that was absorbed by the small holes on the collector plate, thereby enhancing the heat utilization efficiency of the collector plate. The double-sided jet also shared the best performance. The highest outlet temperature (33.12 °C) was achieved at the lowest jet velocity of 1.2 m/s. The optimal structure was determined as a slot width of 10 mm and a double-sided jet mode. The air-curtain jet increased the collector efficiency by 14.57% under a crosswind speed of 0.6 m/s. Narrow slots caused insufficient heat absorption, due mainly to the thin jet layers, while the wide slots caused the heat loss, as the upper part of the thick jet layer diffused into the atmosphere. As such, the double-sided jet with a slot width of 10 mm exhibited the best performance under crosswind conditions, in terms of the thermal efficiency of the collector. Moreover, there was a gradually decreasing effect of the jet on the thermal efficiency as the crosswind speed increased. The velocity of the jet was often required for the optimal outlet temperature. The air-curtain jet can provide a new approach for the USAC to resist environmental interference.