[ Objectives] This study aimed to establish a QAMS (quant. anal. of multi-components by single-marker) method for simultaneous determination of four phenolic acids, salvianolic acid B, tanshinol, lithospermic acid and rosmarinic acid in Radix Salviae Miltiorrhizac by HPLC and conduct methodol. investigation.[Methods] Salvianolic acid B, with moderate retention time, good resolution, great response value and easy availability was selected as the internal standard, and the relative retention values and relative correction factors between tanshinol, rosmarinic acid, lithospermic acid and salvianolic acid B were established.The results of QAMS were compared with those of external standard method to verify the accuracy and applicability of QAMS.[ Results] There were no significant differences between the calculated values of QAMS and the measured values of external standard method.The relative deviation was less than 3%, and the relative correction factors obtained from the experiment were credible.[ Conclusions] QAMS can l>e used to determine the contents of phenolic acids in Radix Salviae Miltiorrliizae formula granules.