This study successfully isolated a novel homogeneous polysaccharide (SRP-W-2) from Streptomyces rochei D74, which exhibited the potential to enhance both growth and tanshinones accumulation in Salvia miltiorrhiza hairy roots. Monosaccharide composition analysis revealed that SRP-W-2 consisted of glucose and galactose, with a molar ratio of 12.53:1, respectively. Methylation and NMR analyses demonstrated that the main chain of SRP-W-2 was composed of (1→4)-α-D-glucose with two O-6-linked branched chains. Notably, PSF-W-1 significantly promoted biomass accumulation in S. miltiorrhiza hairy roots. Furthermore, PSF-W-1 substantially increased the tanshinone content in hairy roots by upregulating the transcript levels of key biosynthetic genes (HMGR, DXS, DXR, and GGPPS). The findings suggest that SRP-W-2 may serve as a potential inducer for the biosynthesis of tanshinones in S. miltiorrhiza hairy roots, thereby meeting the increasing commercial demand for these compounds.