Theoretical models of temperature and thermal stress for Ti-6Al-4V during electrical discharge machining (EDM) process are established. Based on finite element method, the temperature field of EDM Ti-6Al-4V alloy is simulated firstly with the aid of ANSYS, the results can be used to predict the width and depth of the spark crater. The simulated results show that there is a high temperature distribution at the spark point while the zone is quite small. The thermal stress field is estimated using the results of the temperature field as input. Surrounding the spark crater, the thermal stresses are concentrated, where may cause micro-cracks.