Illumination is an important factor for agricultural production. To investigate the effects of shading on plant growth and quality, five shading treatments were applied in triplication including a check (CK), shading of 30%, 50%,70% and 90%, respectively, to a triennial herb species triennial Clematis manshurica. Plants were grown in fields shaded by black plastic screen. Biomass, chlorophyll, photosynthetic characteristics and active ingredients were measured before harvesting. Significant differences in plant growth and herb quality were observed among the treatments. Plant height increased with the increasing of shading fractions. Highest stem diameter and biomasses of the roots and rhizomes of C. manshurica were in shading of 30%, which differed significantly from other treatments. Stem and leaf biomasses in shading of 30%differed greatly from those in CK, shading of 70% and 90%. Organ biomasses of C. manshurica in response to shading varied. Rhizome biomass ratio and root/shoot ratio decreased with the reduction of illumination intensity, while the stem biomass ratio and leaf biomass ratio increased with the reduction of illumination intensity. Biomass of C. manshurica was assigned to stem and leaf growth in order to expand leaf area, absorb the more solar energy and maintain normal growth development under shading conditions. Photosynthetic pigment contents increased with the increasing of shading level, and its contents were the highest in shading of 90%, which differed greatly from other treatments. However, the variation trend of chlorophyll a/b was contrary. The chlorophyll b content of triennial C. manshurica increased with reduced illumination intensity. As a result, the plant could fully absorb scattered light in order to keep higher photosynthetic capacity. This differential effect of shading on the herb plant growth may play an important role in its shade-tolerance. The net photosynthetic rate was 10.86 μmol · m^-2 · s^-1 in shading of 30%, which was significantly higher than other treatments. The stomatal conductance of C. manshurica increased to the maximum and then decreased with the increasing of shading. However, the trend of intercellular CO₂ concentration was contrary. The intercellular CO₂ concentration in the shading of 30% was the minimum, which differed greatly from other treatments. The net photosynthetic rate and the total accumulation of photosynthetic products of triennial C. manshurica decreased with the increasing of shading levels, as a result, sharp decreases in biomass of C. manshurica were observed in the shading of 70% and 90%. The oleanolic acid content of C. manshurica varied with illumination. Severe shading produced unfavorable effects on the growth and accumulation of active ingredient in C. manshurica. And the oleanolic acid content of triennial C. manshurica varied greatly among the treatments and plant growth stages, and higher ones appeared in CK and shading of 30%, which differed significantly from other treatments. In conclusion, the results indicated that the appropriate shading could increase biomass of triennial C. manshurica without decreasing the active ingredient content. We recommended that the best harvest time of triennial C. manshurica should be after August if the production was not for seeds in practice, and this knowledge is essential for formulating generalization regarding the cultivation of the species in Jilin Province, China.