Abstract: Traditional rock breaking techniques face challenges in adapting to the complex geological environment and are limited in efficiency for railway tunnel excavation.Pressurized pulsed water jet combines high pressure and pulse characteristics,offering new theoretical and technical support for efficient hard rock fragmentation.Based on the pressurized pulsed water jet generation method,numerical simulations were conducted to investigate the flow field characteristics and hard rock fragmentation.Firstly,cavitation and turbulence models were revised to support the establishment of a two-stage rock breaking model using flow field data.Secondly,the development of cavitation inside the nozzle and its influence on the jet structure were explored,and the cavitation-vortex interaction was elucidated through vorticity transport analysis,revealing the evolution of various parameters and their impact on jet energy attenuation.Finally,based on smoothed particle hydrodynamics,a two-stage pressurized pulsed water jet rock breaking model was established to quantify the damage evolution of rocks under pressurized pulsed water jet impact and elucidate the rock breaking mechanism.The results show that the revised model more accurately reproduces the flow field characteristics captured in experiments,providing more accurate boundary conditions for pressurized pulsed water jet rock breaking.During the generation and development of pressurized pulsed water jet,significant cavitation phenomena occur inside the nozzle,which reduces the jet diameter and induces vortex generation.Moreover,the propagation speed of stress waves generated by water hammer pressure in the pressurized pulsed water jet is higher axially than radially,and the accumulation of rock damage presents a significant “stepwise” effect during stress wave propagation.Rock damage under pressurized pulsed water jet impact can be divided into four stages:low-pressure continuous stage,pressure surge stage,high-pressure continuous stage,and pressure reduction stage,with shear and tensile failure predominating,especially during the pressure surge and high-pressure continuous stages.These findings can further optimize and improve the theory and technology of pressurized pulsed water jet rock breaking.