Abstract: To address the seasonal mismatch between solar energy supply and heating demand, this study focuses on facility agriculture applications in severely cold regions and investigates the energy performance characteristics as well as the technical and environmental feasibility of a solar heating system with seasonal thermal storage. In cold-climate agricultural areas, heating demand is intensive and highly seasonal, while solar energy resources exhibit strong temporal variability, which to some extent restricts the large-scale application of solar heating systems. Therefore, the development of an efficient solar heating system with seasonal thermal storage is of great significance for improving energy utilization efficiency and reducing dependence on fossil fuels in facility agriculture. Based on a practical solar district heating system operating in Lanzhou, this study adopts a combined approach of experimental investigation and simulation analysis, aiming to provide an engineering-oriented solution for heating in cold regions. The system mainly consists of a solar collector subsystem, a large-capacity seasonal thermal energy storage unit, a water-source heat pump unit, and a terminal greenhouse heating subsystem. A dynamic simulation model of the system was established to describe the transient thermal behavior and energy interactions among different subsystems. The model was validated using measured operational data, with maximum errors of less than 9.2% for the outlet water temperature at the collector field and 4.1% for the water temperature in the seasonal thermal energy storage system, indicating good accuracy and reliability for long-term performance evaluation. The overall operating performance analysis of the system shows that, under an annual total solar irradiation of 1,096.8 MW·h, the annual collected heat of the solar collector subsystem reaches 436.5 MW·h, with an average collector efficiency of 39.8%, demonstrating stable solar energy harvesting capability under cold-climate conditions. The annual heat release from the seasonal thermal energy storage tank amounts to 384.8 MW·h, achieving a heat release efficiency as high as 90.0%, which fully reflects the effectiveness of seasonal thermal storage technology in reducing heat loss and realizing inter-seasonal energy transfer. Through the combined heating mode of seasonal thermal storage and a water-source heat pump with an average COP of 3.98, the system achieves a solar fraction of 82.4%, significantly improving the comprehensive utilization efficiency of solar energy and ensuring a reliable heat supply for agricultural greenhouses during the heating season. Annual performance analysis further indicates that the system performs well under severely cold operating conditions, with a thermal storage efficiency of 83.0% and stable long-term operational characteristics. In terms of environmental benefits, compared with traditional coal-fired boilers, the system achieves a primary energy savings rate of 70.2% and a CO₂ reduction rate of 143.9%, while significantly reducing emissions of SO₂, particulate matter, and NOₓ. The results demonstrate that the solar heating system with seasonal thermal storage has good applicability, operational reliability, and promotion potential in facility agriculture, and also provides a solid theoretical basis for the large-scale application of this technology in urban and agricultural heating scenarios in Northwest China.