Abstract: One-year-old semi-lignified cutting of Platycladus orientalis were immersed in different concentrations of m_IBA∶ m_NAA=1∶1, and the effects of each treatment on 1-year-old semi-lignified cutting of P. orientalis were studied. Improved paraffin section technique was used to study the changes in the external morphology and tissue structure of the cuttings during the development of adventitious roots, which will lay the foundation for the study of the cytological mechanism of adventitious root development. The results show that the best rooting rate of cuttings treat with 80 mg/L m_IBA∶m_NAA =1∶1 for 4 h is 91.38%. Morphological observations reveals that the formation process of adventitious roots could consist of 4 consecutive periods of callus formation, induction, expression, and elongation, which lasts for about 90 days. Anatomical observations show that the root primordium belongs to the induced root primordium. There are no latent roots in the cuttings before cuttings. And callus forms the basis for the formation, growth and development of adventitious roots. It must be induced to form callus before rooting, and belongs to callus induction type. The adventitious root primordium originated from the intersection of the callus and the myelin rays with the formation layer, belonging to multiple sites to take root.