The cDNA sequence of PjHMGR was cloned from Panax japonicus callus and bioinformatics analysis of it was conducted in the study. Overexpression vector pCAMBIA2300sPjHMGR was constructed and then transferred into the P. japonicus callus to obtain the transgenic cell lines successfully by the method of Agrobacterium tumefaciens transformation. The relative expression level of PjHMGR, the enzyme activity of PjHMGR, the contents of PJS and phytosterols in transgenic cell lines were determined by the fluorescence quantitative PCR, colorimetric method and saponification. The results showed that: (1) all of them in PjHMGR transgenic cells achieved enhancements to some extent compared with the control. Especially, the expression level of PjHMGR, the enzyme activity and PJS content of the bestperforming positive cell line were 7.15 times, 6.14 times and 3.50 times of those in control, respectively. Meanwhile, the content of phytosterol in transgenic cell lines was also found to be enhanced. (2) The study considers that if the key enzyme genes (For example: the overexpressing vector of PjHMGR in the biosynthesis pathway, was transformed into Panax japonicus callus, which will increase the relative expression level of the key enzyme genes and the activity of the PjHMGR enzyme, thereby regulating the synthesis of the total saponins of Panax japonicus.) take part in the biosynthesis of saponin were regulated. The regulation of the synthetic pathway of saponin will be realized.