Abstract: Based on the servicing process of the hollow mandrel of the Φ340 mm MPM,a 3-D FE mathematic model is set up.with which the ID dimensions of the mandrel is designed,and the temperature field and surface thermal fatigue of it in servicing process are analyzed.The analysis result reveals the facts as follows.For the hollow mandrel with OD as 358.1 mm,in case of ID as 200~240 mm,balance weight reduction and deformation control are better obtained,while in case of ID as 214 mm,the temperature fields of the hollow mandrel at the three phases i.e.,rolling,the first air cooling and the first water cooling are almost the same as those of the solid mandrel at the same phases.However at the other servicing phases the inner surface temperatures of the former are 13~18 ℃ higher than those of the solid mandrel at the same positions.It is also revealed that the difference between the thermal stress of the hollow mandrel and that of the solid one leads to the result that both the circular and axial cracks of the former are developed earlier,and extended faster than those of the latter.