Flash temperature on the friction surface has serious impacts on the material properties. Thermal differential equation of asperities on the friction surface of tool was established. The factors influencing the temperature in the asperities were analyzed. Flash temperature analytical model was derived under the condition of dry friction and water jet assisted friction based on the concept of surface contact coefficient. Surface contact coefficient based on uniform distribution model and probability distribution model also were presented. Calculation method of friction coefficient under water jet assisted friction which meet dynamic lubrication condition was determined. Computation and infrared temperature measurement results showed that flash temperature on the tool-rock friction surface is heavily dependent on both the contact friction coefficient and the distribution of asperities their surface. The flash temperature calculations obtained by this model is closer to the experimental measurements than the traditional calculation method.
