Tomato is one of the main facility crops in Shandong. It is important to study the effect of light on protected tomato for the production of protected agriculture in Shandong. The experiment takes the infinite-growth-type tomato “Power Corolla” as experimental material to study the protective enzyme activity of tomato leaf under different shading days and the recovery capability of protective enzyme under relighting. Five shading treatments of tomatoes are set in solar greenhouse during the flowering and fruiting period: T1 (3-day shading), T2 (6-day shading), T3 (9-day shading), T4 (12-day shading), and T5 (15-day shading). Moreover, the growth of tomatoes under natural light in solar greenhouse is used as the control check. The results are as follows. Sparse sunlight would increase the protective enzyme activity of tomato leaf and reduce the specific leaf weight. As the number of shading days increases, the recovery capability of protective enzyme activity and specific leaf weight of tomato leaf would reduce. Long shading time (above 12 days) would cause irreversible damage to the photosynthetic system of leaf and make the protective enzyme activity unrecoverable.