The study investigates the quasiparticle dynamics in La$_3$Ni$_2$O$_7$ under high pressure using ultrafast optical pump-probe spectroscopy. At ambient pressure, the relaxation data indicate the appearance of a phonon bottleneck effect due to the formation of a density-wave-like gap at 151 K, with an energy scale of 70 meV. This effect is gradually suppressed by increasing pressure, disappearing around 26 GPa. At pressures above 29.4 GPa, a new density-wave-like order with a transition temperature of approximately 130 K is observed. The results provide the first experimental evidence of density-wave-like gap evolution under high pressure and offer insights into the interplay between density wave order and superconductivity in La$_3$Ni$_2$O$_7$. The findings suggest that both density wave orders coexist with superconductivity, but compete with each other, similar to the behavior in cuprates and iron-based superconductors.The study investigates the quasiparticle dynamics in La$_3$Ni$_2$O$_7$ under high pressure using ultrafast optical pump-probe spectroscopy. At ambient pressure, the relaxation data indicate the appearance of a phonon bottleneck effect due to the formation of a density-wave-like gap at 151 K, with an energy scale of 70 meV. This effect is gradually suppressed by increasing pressure, disappearing around 26 GPa. At pressures above 29.4 GPa, a new density-wave-like order with a transition temperature of approximately 130 K is observed. The results provide the first experimental evidence of density-wave-like gap evolution under high pressure and offer insights into the interplay between density wave order and superconductivity in La$_3$Ni$_2$O$_7$. The findings suggest that both density wave orders coexist with superconductivity, but compete with each other, similar to the behavior in cuprates and iron-based superconductors.