Abstract: The aim of this research is to study the effects of light intensity on the growth,accumulation of active constituents and antioxidant activities of Taraxacum mongolicum. Four light intensity treatments with 80%, 60%, 40% and 20% light transmittance were created, and natural light was set as the control. The biomass, photosynthetic efficiency, the content of active constituents and antioxidant activity were measured after 30 d treatment. The results showed that 60% light transmittance promoted the growth and accumulations of photosynthetic products, and the highest leaf area, leaf numbers, the biomass of the above ground and under ground, the net photosynthetic rate, the electron transportation rate, the accumulation of assimilation products were also obtained in these light condition. The light transmittance less than 40% decreased the accumulations of active constituents, especially the total triterpenoid. The content of the total flavonoid, the total phenol, the total choline were increased initially with the light transmittance decreasing, and then decreased, and the highest contents of the total phenol was occured in the 60% light transmittance, while the highest content of the total flavonoid and choline were obtained in the 80% light transmittance. A correlation analysis suggested that the scavenging ability of free radicals were positive correlated with the contents of active ingredients, among of these, DPPH free radical scavenging ability showed a positive correlation with the content of total flavonoid, total triterpenoid, the total phenol, and the total choline, ABTS⁺ free radical correalated with total phenol positively, OH^- free radical scavenging ability were also significantly related to the content of the total choline and the total phenol. With a comprehensive comparison of yield and the contents of active constituents, T.mongolicum grow in 60%-80% light transmittance could obtainted a high yield and quality.