Abstract: Rock-breaking by high-pressure water jet is a non-linear dynamic problem with many influencing factors. Aiming at the instantaneity of rock-breaking process by jet and the problem of avoiding mesh distortion in finite element method, the rock-breaking process by continuous jet is simulated based on ALE algorithm. Jet and air adopt ALE format and rock adopt J-H-C model. Then the rock-breaking mechanism, rock failure form and rock damage by high-pressure water jet are analyzed. Characteristics of injury. The results show that rock fragmentation is the result of the combined action of impact pressure, water hammer pressure, stress wave and water wedge. Rock fragmentation by jet has periodic cyclicity, and each mode of action has corresponding dominance in different stages of rock fragmentation cycle. The failure mode of rock is time-varying. At different times, the failure mode changes constantly, and the final failure mode is funnel-shaped or deep "V" shaped. Rock damage has stages, which can be divided into non-damage stage, intensive damage stage and failure stage. Rock failure has local characteristics and zoning, which can be divided into damage zone, damage zone and original state zone.