Abstract: Taking Fraxinus americana cuttings as the research object, the changes of endogenous hormones and enzyme activities in the process of rooting were explored, and rooting mechanism was studied. The rooting of Fraxinus americana cuttings was observed and recorded, and the contents in the rooting process were dynamically determined with the cutting base as the material. Results showed that, rooting types of Fraxinus americana cuttings were mostly originated from cortex primordium, few were callus rooting type. The rooting process can be divided into three stages: root induction period（0-12 days）, adventitious root expression period（12-24 days）, and adventitious root elongation period（after 24 days）. The study of endogenous hormones showed that the content of IAA and IAA/ZR increased first and then decreased; the content of ABA in the treatment group and GA₃ in the control group showed a double peak trend; the change trend of ZR and IAA/ABA ratio was firstly decreased and then increased. The oxidase activity study found that the activities of peroxidase（POD） and indoleacetic acid oxidase（IAAO） showed an increase to decrease to increase trend, while the activities of polyphenol oxidase（PPO） showed an increase to decrease trend. It can be concluded that the use of NAA increased the content of ABA, and decreased the content of GA₃ and the value of IAA/ABA. PPO and POD with high activity were beneficial to the induction of root radical, while IAAO with high activity was beneficial to the elongation of adventitious roots.