Dynamic fracture toughness of Laurentian granite (LG) subjected to heat treatment was tested by means of a notched core-based semi-circular bend (SCB) specimen with a modified split Hopkinson pressure bar (SHPB) apparatus. The samples for testing the fracture toughness were manufactured and heat treatment up to 850D according to the requirements of experiment. The relationship between the fracture toughness and temperature were investigated of rocks subjected to thermal treatment. The experimental results showed that fracture toughness decreases with increasing temperature. Furthermore, the fracture surfaces of rocks in thermal treated were observed by means of the scanning electronic microscope (SEM). These results provide the theoretic direction for engineering application in thermal treatment.