Ultrafast optical spectroscopy reveals density-wave-like gap evolution in La3Ni2O7 under high pressure. The study uses ultrafast pump-probe spectroscopy to investigate quasiparticle dynamics in La3Ni2O7 under pressures up to 34.2 GPa. At ambient pressure, the temperature dependence of relaxation indicates the appearance of a phonon bottleneck effect due to the opening of a density-wave-like gap at 151 K. The energy scale of the gap is identified as 70 meV. The relaxation bottleneck effect is gradually suppressed by pressure and disappears around 26 GPa. At pressures above 29.4 GPa, a new density-wave-like order with a transition temperature of ~130 K is discovered. These 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 La3Ni2O7. The study shows that the density wave order is gradually suppressed under pressure, leading to a decrease in gap amplitude from ~70 meV at ambient pressure to ~20 meV at 13.4 GPa, and then remains constant before vanishing at 26 GPa. The emergence of a new density-wave-like order at pressures above 29.4 GPa is likely related to charge density wave order. The results also indicate that superconductivity coexists with density wave orders in La3Ni2O7, though it competes with superconductivity in the DW I region, similar to cuprates and iron-based superconductors. The study highlights the sensitivity of the pump-probe technique to the presence of density wave-like order.Ultrafast optical spectroscopy reveals density-wave-like gap evolution in La3Ni2O7 under high pressure. The study uses ultrafast pump-probe spectroscopy to investigate quasiparticle dynamics in La3Ni2O7 under pressures up to 34.2 GPa. At ambient pressure, the temperature dependence of relaxation indicates the appearance of a phonon bottleneck effect due to the opening of a density-wave-like gap at 151 K. The energy scale of the gap is identified as 70 meV. The relaxation bottleneck effect is gradually suppressed by pressure and disappears around 26 GPa. At pressures above 29.4 GPa, a new density-wave-like order with a transition temperature of ~130 K is discovered. These 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 La3Ni2O7. The study shows that the density wave order is gradually suppressed under pressure, leading to a decrease in gap amplitude from ~70 meV at ambient pressure to ~20 meV at 13.4 GPa, and then remains constant before vanishing at 26 GPa. The emergence of a new density-wave-like order at pressures above 29.4 GPa is likely related to charge density wave order. The results also indicate that superconductivity coexists with density wave orders in La3Ni2O7, though it competes with superconductivity in the DW I region, similar to cuprates and iron-based superconductors. The study highlights the sensitivity of the pump-probe technique to the presence of density wave-like order.