Abstract: Hybrid rice Chuanxiang 9838 with medium shade-endurance was taken as the test material to investigate the effects of different sowing dates and  low-light stress at heading stage on the flag leaf photosynthetic rate (P_n), osmotic regulators, antioxidant enzyme activities  and the grain yield of hybrid rice. Sowing date and  lowlight stress at heading stage had significant effects on the flag leaf P_n and antioxidant enzyme activities and plant dry matter accumulation at heading stage and the grain yield. With the delay of sowing date, the whole period of rice growth and development shortened notably, and the grain yield decreased to different degrees.  Compared with the control, short-term slight low-light stress (20% shading) at heading stage could relieve the harms from high temperature and strong light, and further, relieve the decrease of flag leaf P_n and plant dry matter accumulation at heading stage, adjust the flag leaf antioxidant enzyme activities, and moderately improve the seed setting rate. However, short-term medium low-light stress (40% shading) and serious lowlight stress (60% shading) were not beneficial to the rice growth. Correlation analysis indicated that the flag leaf P_n, malondialdehyde (MDA) content, and superoxide dismutase (SOD) were more sensitive to the sowing date and  low-light stress at heading stage, and there existed a highly significant positive correlation between the flag leaf P_n at initial heading stage  (1-5 d) and the plant dry matter accumulation at late heading stage and grain yield.