Abstract: Due to the complexity of rock breaking by particle-waterjet impact and the transient rock breaking process, there is always a difficulty in studying the rock mechanical properties and failure damage under particle waterjet impact. Considering the influence of particle jet backflow, based on the cavity expansion theory, a mathematical model of rock stress and rock breaking region under the coupling impact of particle waterjet is established. The influence law of particle size and jet velocity on rock stress distribution and rock-breaking region under single particle jet impact is analyzed by mutual verification between numerical analysis and simulation. According to the rock breaking process by multi-particle waterjet under coupling continuous impact, this study proposes the calculation method of rock breaking region. The rock breaking region laws under the condition of vertical jet and rotating jet are obtained through numerical calculation and experimental verification. The results show that the rock-breaking area with rotating jet at a certain angle is larger than that with vertical jet during rock breaking under particle-waterjet coupling impact. The increase of particle diameter has little influence on the rock-breaking area. When the waterjet impact velocity is 200 m/s and the particle size is 1.0 mm, the rock breaking area impacted by 8° and 20° waterjet is 1.7 and 1.9 times greater than the diameter of nozzle outlet respectively.