By integrating pump-probe ultrafast spectroscopy with diamond anvil cell (DAC) technique,we demonstrate a time-resolved ultrafast dynamics study on non-equilibrium quasiparticle (QP) states in Sr2IrO4 under high pressure.On-site in situ condition is realized,where both the sample and DAC have fixed position during the experiment.The QP dynamics exhibits a salient pressure-induced phonon bottleneck feature at 20 GPa,which corresponds to a gap shrinkage in the electronic structure.A structural transition is also observed at 32 GPa.In addition,the slowest relaxation component reveals possible heat diffusion or pressure-controlled local spin fluctuation associated with the gap shrinkage.Our work enables precise pressure dependence investigations of ultrafast dynamics,paving the way for reliable studies of high-pressure excited state physics.