This paper presents a novel solar thermal facade system able to employ renewable energy to relieve building energy consumption. The flat-plate collector, reflection layer, main wall, and indoor radiation plate were designed so as to avoid overheating and create a suitable indoor thermal environment for a hot-summer and cold-winter zone. The thermal performance of the facade system was tested under different conditions in typical summer and winter days. The novel solar facade system makes use of solar energy and a water supply to improve an indoor thermal environment with little temperature fluctuations. Compared with tests under stagnation conditions, the average temperature of indoor air was reduced by 8.9 degrees C under cooling conditions and increased by 8.0 degrees C under heating conditions. Validated by experimental results, theoretical calculations were performed to further optimize the system. Finally, the effect of parameters, such as outdoor climate, inlet water of the radiation plate, and main wall on the thermal performance, was assessed and the corresponding conditions to achieve a suitable indoor temperature were analyzed. This work is helpful for the energy-saving design of building-integrated solar thermal systems.