Abstract: Abstract: A Solar Air Collection (SAC) has been well known as one of the most developed technologies in solar energy industry. Therefore, the SAC heat exchanger has also been widely used to convert the solar radiation into heat energy in a broad range of fields, such as space heating and crop drying. However, the SAC utilization depends mainly on the high density and heat capacity of air, particularly for the better heat transfer between flowing air and absorption plate. Therefore, the high intensity of heat transfer can be improved by increasing the absorption areas and enhancing the turbulence in the collector cavity. Much effort has been made to improve the thermal performance of solar collector, particularly by changing the structure of the absorption plate or the flow channel in the cavity. Specifically, some new structures were proposed to increase the surface roughness, such as V-fins, W-fins, and hemispherical grooves. Furthermore, some staggered fins and baffles were added to introduce the swirling flow for the higher turbulence intensity in the collector cavity. These technologies can be utilized for the better SAC performance of the absorption plate and the air flow. In addition, the jet impact can also be expected to improve the heat exchange intensity of the collector, while the unglazed collector can be used to reduce the reflection loss of heat radiation. But, the main heat loss on the bare cover plate depends mainly on the external wind speed. Therefore, it is necessary to further promote the heat exchange intensity in the unglazed collector, in order to speed up the air in the cavity to take away the heat on the heat absorbing plate, particularly for the reduced heat loss on the plate. In this study, an optimal unglazed solar air collector was proposed for the higher efficiency of heat collection using the U-tube reverse jet for the heat exchange of the collector plate. A systematic experiment was carried out to explore the temperature distribution inside the collector and the heat collection performance under the typical winter and summer conditions. The experimental results show that the optimal cooling performance of reverse impinging jet was achieved to effectively reduce the surface temperature of the collector, particularly for the low-temperature area covering most of the area of the heat absorbing plate. The relatively uniform temperature distribution was greatly contributed to reduce the heat loss of the collector. The U-shaped tube as the reverse jet was also utilized to introduce the additional function for the air preheating, when entering the collector chamber. The relatively small temperature difference of 3.5 ℃ was found between the inlet and outlet of the U-shaped tube under the typical working conditions. The average efficiency of heat collection reached 80% on the typical working days in summer, while only 45% was obtained in winter. Consequently, the finding can provide a new idea for the performance optimization of solar collector without cover plate.