The first-order Raman spectroscopy of diamond exhibits splitting and redshift after the burst of high-pressure (160–200 GPa) and high-temperature (～2000 K). The observed longitudinal optical (LO) and the transverse optical (TO) splitting of Raman phonon is related to the tensile-strain induced activation of the forbidden or silent Raman modes that arise in the proximity of the Brillouin zone center.