In order to estimate the energy partition within the workpiece, an integral approximation solution of energy partition is found in the grind-hardening process. Heat transfer models of the abrasive grain, workpiece, chips and fluid were analyzed by using the integral approximation method. The present model can calculate the energy partition with and without film boiling in the grinding zone. The temperature underneath the surface of the workpiece was measured using semi--natural thermocouple method. The workpiece background temperature calculated by the present model agreed very well with the experimental results. Energy partition model can be used to calculate the grinding temperature for controlling thermal damage and predicting the harden layer depth in grinding.