In this study, Bupleurum chinense was used as material, and the PEG6000 nutrient solution with a mass fraction of 10% and 20% was used to simulate drought stress experiments. The contents of endogenous signal substances OPR and JA, the expression of transcription factor BcMYC2 and the key enzyme genes in the saikosaponin biosynthesis pathway, and the contents of saikosaponin a and d were detected for exploring the mechanism of jasmonic acid signaling pathway regulating BcMYC2 and affecting saikosaponin biosynthesis under simulated drought stress. The results showed that: (1) after PEG6000 was used to simulate drought stress to treat the seedlings of Bupleurum chinense, the OPR content in the 20% PEG6000 treatment group showed a peak at 2 h, and the OPR content of the 10% PEG6000 treatment group peaked at 6 h. However, the endogenous JA peaked at 2 h for both treatments. (2) In both treatment groups, the relative expression of BcMYC2 show a peak at 2 h and then decreased significantly in 2-4 h, and the relative expression of BcMYC2 in 20% PEG6000 group was higher than that in 10% PEG6000 group. The relative expression of HMGR, IPPI, FPS and βAS of the other four key enzymes of saikosaponin biosynthesis pathway reached the peak at 4 h. The peak time of relative expression of BcMYC2 was earlier than the relative expression of these key enzyme genes. (3) Saikosaponin content in seedling roots gradually increased within 36 days after simulated drought stress. At 36 days, the content of saikosaponin in the 20% PEG6000 treatment group was slightly higher than that in the 10% PEG6000 treatment group. Studies have shown that after PEG6000 simulated drought treatment, the contents of signal substances OPR and JA in Bupleurum chinense DC. seedlings increased, which promoted the expression of BcMYC2, thereby increasing the expression of key enzyme genes in the saikosaponin biosynthetic pathway and ultimately affected the content of saikosaponin in roots.