Abstract: In order to analyze the response mechanism of forest window size on the growth and photosynthetic physiology of mokoro planted in the understory of Caesalpinia equisetifolia to the forest window area, the following experimental materials were used. We took 2-year-old mokoro seedlings as experimental materials, set up different forest window treatments without opening forest windows (CK) and with forest window areas of 50 m² (T₁), 100 m² (T₂), 200 m² (T₃), and 400 m² (T₄), and analyzed the effects of different forest window areas on mokoro's growth and photosynthetic indexes. The results showed that the increase of forest window area increased the relative air temperature and decreased the relative humidity inside the forest window; the different area of forest window in different seasons had a significant effect on the height, diameter and biomass of mokoro seedlings, which showed winter<autumn<summer in seasons, and the highest value of the growth in summer (July) was in the T₄ treatment (47.42 cm), and the lowest value was in the CK treatment (16.52 cm), and the highest value was in the CK treatment (16.52 cm), and the lowest value was in the CK treatment (16.52 cm). different forest window treatments were CK < T₁ < T₂ < T₃ < T₄, and T₄ was significantly different from T₁ and CK (P < 0.05); the net photosynthetic rate (P_n) and stomatal conductance (G_s) of mokoro leaves reached the highest value at T₄ treatment in summer, which were 9.95 μmol/(m²·s) and 0.09 μmol/(m²·s), and carbon dioxide CO2 (C_i) and transpiration rate (T_r) varied in a V-shape with the increase of the forest window area; whereas, all the treatments of forest window size did not have significant effects on the maximal fluorescence efficiency of the PSII reaction centers (F_v/F_m) and the potential fluorescence activity (F_v/F₀)); There was a significant negative correlation between temperature and humidity (P<0.05), tree height, ground diameter and Pn were significantly negatively correlated (P<0.05), ground diameter and Tr and Gs were significantly negatively correlated (P<0.01), and Pn and Gs, and tree height and tree height were significantly negatively correlated (P<0.001). From the perspective of growth and photosynthesis, the forest window area of 400 square meters was more conducive to the growth of S. superba and met the growth conditions of S. superba with strong light-loving growth.