We selected Chinese fir seedlings to study the effects of light intensity on seedling growth, morphology, biomass, biomass allocation, and non-structural carbohydrate (NSC) content in the leaves using a shade house experiment (100%, 60%, 40%, 15%, and 5% of full sunlight). The results showed that:(1) The greatest leaf length, leaf width, and leaf area occurred under 40% sunlight, whereas the specific leaf area and relative water content increased as light intensity decreased; (2) As light intensity decreased, the total biomass, root biomass, stem biomass, and leaf biomass of seedlings declined, the stem biomass ratio and leaf biomass ratio increased, and the root biomass ratio and root to shoot ratio decreased; (3) The greatest and lowest NSC content occurred under 60% and 5% sunlight, respectively; (4) The specific leaf area was significantly negatively correlated with leaf biomass and NSC content (P < 0.01), whereas leaf biomass had a strong positive correlation with NSC content (P < 0.01). In summary, Chinese fir seedlings might adapt to a shaded environment by adjusting their morphological characteristics to improve their competitive ability and fitness, although seedlings had difficulty maintaining a carbon balance, which led to poor growth and survival, under 5% sunlight.