In face of global climate and environment change, the North China is experiencing the increasing trend of mean temperature and the pattern change of precipitation, resulting in more and more severe volatility in regional soil water contents. This phenomenon may significantly affect the photosynthesis, growth and productivity of plants in the region. The objective of this study is to explore the photosynthetic and physiological characteristics of Forsythia suspensa (Thunb.) Vahl. under different soil water conditions and various light intensities in both spring and summer. With the quantified relationship between the photosynthesis and soil water content in both seasons, this study can help understand the responsive and adaptive characteristics of Forsythia suspensa for more severe and longer droughts that may occur as a result of regional climate change in the North China. By using a Li-6400 portable photosynthetic system, the light response processes of the two-year Forsythia suspensa under multiple controlled soil water content treatments in both spring and summer were measured and analyzed. The response of photosynthetic parameters under both low light and saturated light conditions in spring and summer were also investigated. The results show that the photosynthetic characteristics of Forsythia suspensa are related to the photosynthetically active radiation (PAR), the relative soil water content (SRWC) and the periods of plant growth and development. First, when PAR≤200 μmol m^-2 s^-1, the light responses of net photosynthetic rate (Pn), stomatal conductance (Gs), and water use efficiency (WUE) were not sensitive to seasons, while the responses of Pn and Gs were related to both soil water contents and seasons in strong light, and their differences between spring and summer appeared to be significant when the SRWC>40%. When the SRWC≤32.41% in spring and SRWC≤38.65% in summer, Pn and Gs maintained lower level when PAR increased from 0 to 1800 μmol m^-2 s^-1. Second, when 37.52%≤SRWC≤42.55% or 64.10%≤SRWC≤92.97% in spring, photo-inhibition occured, while no photo-inhibition was observed in summer when PAR changed from 0 to 1800 μmol m^-2 s^-1, indicating the occurrence of photo-inhibition was also related to periods of plant growth and development. Third, the apparent quantum yield (φ), Pn, WUE, Gs, intercellular CO₂ concentration (Ci), and stomatal limitation value (Ls) in both seasons have similar response to soil water content, while the soil water content thresholds of the parameters were different between spring and summer, indicating the importance of soil water content thresholds in the seasonal difference of light responses. Finally, the optimal soil water content (SRWC) range was from 51.84% to 58.96% in spring and from 52% to 83.34% in summer in which Forsythia suspensa has relatively high Pn, Gs, WUE and φ, and in which no significant photo-inhibition was observed, and the optimal light intensity (PAR) range for photosynthesis was from 1000 μmol m^-2 s^-1 to 1400 μmol m^-2 s^-1 in both seasons. Therefore, it is necessary and crucial to determine the optimal ranges and critical thresholds of environmental parameters (soil water content, light intensity, temperature, CO₂ concentration, etc.) according to the growing seasons of plants, which can serve for better regional adaptation practice of climate and environment change.