• The rock breaking process by high-pressure water jet on thermal rock is divided into four distinct stages: initial fluid-solid contact, intense thermal exchange, perforation and fracturing, and crack propagation and penetration.
• Increasing rock temperature significantly reduces jet reflection angles and cooling time, while enhancing crack number and propagation rate, shortening critical breaking time by up to 34.5%.
• Numerical simulations show that the center temperature of granite at 400 °C drops from 390 °C to 260 °C within 0.7 seconds under jet impact, indicating rapid thermal exchange.
• A critical temperature and critical heat flux prediction model was established to describe the staged breaking of hot rocks, offering guidance for deep geothermal rock excavation.