[Objective] With the background of the forest-medicine compound planting mode of Acer Truncatum forest and Platycodon grandiflorum in Beijing, we explored the potential effects of A. Truncatum fallen leaves extracts on the accumulation of major medicinal active ingredients in the roots of P. grandiflorum. Transcriptome sequencing was performed on the roots of P. grandiflorus to identify differentially expressed genes and metabolic pathways, which is of great significance for revealing the molecular mechanisms in the synthesis pathway of active ingredients in P. grandiflorum roots. [Methods] Using Illumina to perform transcriptome sequencing on the roots of P. grandiflorus, evaluate the gene expression changes and deeply explore the synthesis pathways of terpenoids, flavonoids, and phenylpropanoid secondary metabolites. [Results] 753 DEGs were annotated into the three major classes in GO classification, and 402 DEGs were annotated into the 50 metabolic pathways of the KEGG database. Compared with the control group, there were 17, 7, and 26 DEGs involved in the biosynthesis of terpenoids, flavonoids, and phenylpropanoids, respectively. [Conclusion] In the terpenoid biosynthesis pathway, 10HGO, CYP71D55, CYP76F14, and LUS showed up-regulated; in the flavonoid synthesis pathway, the identified DEGs showed an overall up-regulated; in the phenylpropane synthesis pathway, COMT was down-regulated, 4CL and REF1 were down-regulated, and the DEGs overall were down-regulated expression. It is presumed that the synthesis of terpenoids and flavonoids increased and the synthesis of phenylpropanes decreased. The article obtained the full transcriptomic information of the roots of P. grandiflorum and preliminary predicted the possible regulatory pathways for the synthesis of terpenoids, flavonoids, and phenylpropanoid in P. grandiflorum.[ ][ ]