Abstract: Thermal mechanical fatigue behavior of 316 LN stainless steel is studied by thermal mechanical fatigue test, the fatigue data and curve are obtained. The result shows that 316 LN stainless steel has a hardening and then softening process during the whole life. The hysteresis loop is fusiform, which means a well plastic deformability. With the increasing of the temperature, the deformability is enhanced and the fatigue characteristic is more distinct. Under the operation condition of the surge line（temperature is less or equal to 320℃）, the strain has the primary effect on the fatigue life. The fatigue life under the 120~320℃ and 120~230℃ conditions is longer than the low cycle fatigue life under constant temperature 350 ℃, which means that the traditional test data of low cycle fatigue under high temperature is too conservative to assess the thermal mechanical fatigue life of the surge line.