Abstract: Abstract: In order to provide cultivation techniques reference for improving the essential oil contents and components of fennel, our research took Inner Mongolia fennel as materials, and Hoagland nutrient solution as base fertilizer, designed 5 different manganese application levels [0 mg/L(CK), 22.3 mg/L(N1), 44.6 mg/L(N2), 66.9 mg/L(N3) and 89.2 mg/L(N4) respectively]. Based on sand culture method, this paper explor the effects of different manganese levels on the fennel growth, chlorophyll content, soluble sugar content, soluble protein content, and essential oil contents and components. The results showed that: the plant heights of treatment N1-N4 were higher than contrast (2.4, 6.0, 6.8, 9.4 cm respectively). Fresh weight and dry matter weight of shoot of treatment N1 were the highest [(71.65±4.79), (8.15±0.73) g respectively]. Besides, more manganese applying, total nitrogen, total carbon, chlorophyll content, soluble protein content of fennel were increased at the beginning, and then became lower. The effects of different manganese applications on essential oil of fennel mainly turn to the relative content of (E)-anethole, and the best treatment was N1. Treatment N1 could promote the growth and improve the relative content of (E)-anethole and terpinolene of fennel.