Effects of shading on photosynthesis characteristics and leaf anatomical structure of Cercidiphyllum japonicum seedlings were researched. Four shade treatments including full sunlight (L₀), 55% sunlight (L₁), 25% sunlight (L₂) and 10% sunlight (L₃) were set. The results showed that: (1) shading had an significant effect on daily variation characteristics of photosynthesis of seedlings. The changes of P_n under L₁ treatment were similar to L₀, and showed rough “乁”shape, and the “noon break” did not appear in the course of the day, and the peak value appeared at 14:00 AM, that of other treatments was relatively mild, and the peak value appeared at 12:00 AM. The variation curve of G_s similar to _Pn, and C_i showed the basically concave change. (2) The order of daily average of P_n, G_s and T_r was L₀ > L₁ > L₂ > L₃, and the order of C_i was versa. Correlation analysis showed that P_n was positively correlated with G_s, T_r, T_a and photosynthetically active radiation (PAR) (P < 0.01). (3) The photosynthesislight response characteristics under different treatments were obviously different. Under full sunlight, the light compensation point (LCP), light saturation point (LSP) and dark respiration rate (R_d) of seedlings were significantly higher than that under shading. The seedlings can maintain high P_n without obvious light inhibition, and C. japonicum seedlings had the ability of light tolerance in a certain degree, and showed the property of light demander. Shading resulted in a significant decrease of LCP, LSP and R_d, which was conducive to the growth of seedings under low light conditions. (4) Shading significantly affected the stomatal distribution on leaf surface. Under shading treatments, the stomatal density was smaller compared with the control, but the length of stomata, width of stomata and single stomatal area increased significantly. The percentage of stomatal area reduced, which will affect water and gas delivery between inside and outside of the seedling cells. (5) Under shading, the leaf thickness decreased, the upper epidermis thickened and the lower epidermis thinned. The thickness of palisade tissue (PT) decreased, sponge tissue (ST) was increased, and the PT/ST decreased accordingly. (6) Shading affects the growth form of C. japonicum seedlings. Compared with the control, the seedlings growth were inhibited under intensive shading(L₂ and L₃), the height(H) and basal diameter(D) decreased, and D₂H dwindled accordingly, while the mild shading (L₁) had no significant effects on H, D, H/D and D₂H of seedlings. So the ecological width of C. japonicum seedlings to the light was wide. In forest seedlings production, moderate shading is beneficial to reduce air temperature and reduce transpiration, but the PAR in the field should be kept above 55% of natural light intensity.