Abstract: 【Objective】 To study weed-inhibiting effect of Cinnamomum longepaniculatum（Gamble）N. Chao ex H. W. Li essential oil from the perspective of allelopathic effects，so as to lay a foundation for developing weed-inhibiting products of C. longepaniculatum essential oil.【Method】 Seeds of Echinochloa crusgalli（L.）Beauv.，Portulaca oleracea L. and Melilotus officinalis（L.）Pall. were used as research objects， and indoor filter paper culture dish method was adopted. C. longepaniculatum essential oil（purity≥99%）and its monomer 1,8-cineole（purity≥98%）were mixed with Tween-80 to prepare solutions of different volume concentrations（0，0.5，1.0，1.5，2.0，2.5，3.0，4.0 and 5.0 μL/mL）for treatments of seeds. With seeds in distilled water was as control，seed germination（germinative energy and germinative rate），amylase activity，seedling growth（plant height，radicle length，root activity）and other indexes were determined to analyze allelopathic effects of C. longepaniculatum essential oil on weed seed germination and seedling growth.【Result】 The treatment of C. longepaniculatum essential oil and 1,8-cineole greatly inhibited germinative energy，final germinative rate， growth and root activity of E. crusgalli，P. oleracea and M. officinalis seeds，and the higher the concentration of the treatment，the stronger the inhibiting effects. The treatment of C. longepaniculatum essential oil lowered mitotic speed of M. officinalis root tip cells，resulting in inhibition of radicle elongation and root hair formation of seedlings. The treatment of C. longepaniculatum essential oil and 1,8-cineole of a certain concentration inhibited amylase activity during seed germination， and an obvious dosage effect was found. The treatment of C. longepaniculatum essential oil and 1,8-cineole significantly increased malondialdehyde（MDA）content in the 3 kinds of weed seedlings（P<0.05），indicating that their cell membrane system was damaged. Synthetical allelopathic index analysis showed that E. crusgalli and P. oleracea were more sensitive to 1,8-cineole，whereas M. officinalis was more sensitive to C. longepaniculatum essential oil.【Conclusion】C. longepaniculatum essential oil and 1， 8-cineole has significant allelopathic inhibiting effects on seed germination and seedling growth of the 3 kinds of weed（E. crusgalli，P. oleracea and M. officinalis）. The inhibiting effects of C. longepaniculatum essential oil partly come from function of 1,8-cineole. But it is also affected by other substances in C. longepaniculatum essential oil，and different kinds of weeds are differently sensitive to various allelopathic components in C. longepaniculatum essential oil.