Abstract: The P-S-N curve of fatigue at low temperatures is the design basis against fatigue of welded components in winter. The fatigue life of welded components at -25℃ temperature was measured on PLG-300 kN high-frequency fatigue testing machine at four stress levels, and the S-N curve of welded components was derived. The P-S-N curve of fatigue at low temperatures was theoretically obtained by using the method of single side tolerance analysis of small-number specimen experiments and the experiential C_V value of logarithmic fatigue life (lgN ) of welded components. This method is a simple and economic one, but its perfection needs more experimental data.