Abstract: Utilizing reliable and hermetic expander with internal generator is an important development direction of organic Rankine cycle (ORC). It is simple and feasible to use the expander exhaust to cool the generator in hermetic expander. However, the exhaust temperature of the expander in ORC system is relatively high, and the cooling effect on the generator needs to be studied specifically. In this paper, an equivalent thermal circuit model of the generator was established based on the lumped parameter concept. The variations of the highest temperature and temperature rise of the stator winding under different working conditions were revealed. Results show that the highest temperature and temperature rise of the generator increase with the improvement of evaporation temperature, reaching 151 ℃ and 85 ℃, respectively. The highest temperature and temperature rise of the generator decrease with the increase of condensation temperature. If the condensation temperature is set to be 30 ℃, the maximum temperature and temperature rise can reach 126 ℃ and 65 ℃, respectively.