Abstract: To evaluate the cold crack sensitivity of welded joints in copper-rich nanophase-strengthened steel with ultra-low carbon and 1 000 MPa grade, a systematic study was conducted by theoretical calculation and inclined Y-shaped groove welding crack tests. The composition applicability range of existing cold crack sensitivity formulas was analyzed. According to the characteristics and the composition range of the nanophase-strengthened steel and the results of inclined Y tests, a new cold crack sensitivity formula was proposed to evaluate the cold crack tendency of the nanophase-strengthened steel with ultra-low carbon. The influence of preheating temperatures on the cold cracks of welded joints was investigated, and a preheating temperature for welding was determined. The results show that the cold crack sensitivity index of the copper-rich nanophase-strengthened steel with ultra-low carbon and 1 000 MPa grade is 0.252. There are no cracks in the base metal and heat-affected zone under the condition of no preheating welding, indicating that the steel plate has excellent welding properties. The cold crack sensitivity of welded joints is significantly reduced with the elevation of pre-weld preheating temperature. When the preheating temperature is 105 ℃, the crack rates in the test welds and heat-affected zone are 0.