Tryptophan is an important amino acid for protein synthesis. It is also the precursor of plant growth hormone IAA and some secondary metabolites, and plays an important role in plant growth and development as well as insect and disease prevention. In order to explore the effect of tryptophan on the growth and development and defense substance accumulation of Chinese cabbage type rapa (Brassica rapa L) and its possible mechanism. In this study, exogenous tryptophan was used to spray the leaves of rapa seedlings, and the effects of tryptophan on the growth and development of rapa seedlings and the synthesis of auxin IAA and secondary metabolites, glucosinolates, were analyzed. The results showed that: (1) the treatment with low concentration of tryptophan (100 mg/L) could effectively promote the development of leaves and roots of rapa, but with the increase of concentration, the promotion effect was gradually weakened. (2) Fluorescence quantitative PCR analysis showed that, after exogenous tryptophan treatment, the three synthesis pathways of auxin IAA in rape seedling leaves were activated, the key enzyme genes BrTAA1 and BrYUCCA8 in the IPA pathway, BrAMI1 in IAM pathway and BrCYP71A13 and BrNIT2 in IAOx pathway, were strongly induced and upregulated. Thus, the content of IAA was significantly increased. (3) Exogenous tryptophan treatment also activated the expression of the downstream such as BrTGG1 and BrPEN2. The altered expression of these genes resulted in the accumulation of indole glucosinolates. The study found, the exogenous tryptophan treatment can effectively promote the accumulation of growthregulating substances and biodefense substances in rapa by regulating the synthesis pathway of IAA and the expression of genes related to the synthesis pathway of indole glucosinolates, thus increasing biomass and improving potential disease resistance.