This experiment was conducted to explore the effects of different light length on plant growth, content and component of essential oil in fennel using the method of shading. The experiment included three kinds of light length treatment: shading at 15:00, shading at 17:00 and no shading. The results showed that plant height, number of nodes and fresh weight of fennel plants shaded at 17:00 were the highest, the plants not be shaded were the second, and the plants shaded at 15:00 were the lowest. Plant dry weight, total carbon content, soluble sugar content, Chl.a, Chl.b and CAR. contents and Chl.a/b were all elevated with light length increased, while total nitrogen and proteinic nitrogen contents were contrary to that. Essential oil content and yield per plant were increased with increase of light length, and that, it was significant difference among the three treatments.Twenty-two essential oil compounds were identified, and there were no difference among different treatments.Most of the essential oil component and their relative amount were no significant differences. The content of (E)-anethole, the dominant essential oil compound, was 47.40% to 48.51%, limonene,the second essential oil compound, was 31.69% to 33.26%, there were no significant differences in three treatments.