By using the combined ultrasonic interferometry and X-ray diffraction method, the elastic wave velocities of aragonite were measured for the first time at pressure and temperature up to 5.8 GPa and 1173 K by using a hot-pressed polycrystalline specimen. Aragonite has has extremely low compressional (Vp) and shear (Vs) wave velocities and V_P, low V_S and high VP/VS ratio than those of the major minerals of subduction slabs. According to the average content of CO₂ in the subduction zones, the velocities of carbonated-eclogite and carbonated-peridotite in both cold and hot subduction zones were modeled. It was revealed that an increase of 2.5 wt% CO₂ resulted in to 2% reduction in Vp and Vs and an increase of Vp/Vs. Our results show that the velocity effect of aragonite in subduction zone can’t be ignored and shed lights on the mechanism of low velocity layers (LVL) in the subduction zones.