The invention provides a red paeony root active constituent which is obtained by the steps of pulverization and heating extraction of red paeony roots, concentration, reverse-phase column separation, elution and concentration and drying of eluent. The red paeony root active constituent provided by the invention can be applied to preparing medicaments for treating and preventing cardiovascular diseases. The preparation method of the red paeony root active constituent, provided by the invention, has reasonable design, can rapidly and accurately obtain the active constituent and is easier for quality control of the medicaments in production.