Abstract: The implant test was used to study the cold cracking sensitivity of manual electrode welding of Q690 high strength steel, and the influence of preheating temperature and welding line energy on the critical fracture stress of Q690 was evaluated.The results show that the critical fracture stress is only 650 MPa when the line energy of 1.48 kJ/mm is used for non preheating welding, while the critical fracture stress is increased to 930 MPa when the line energy of 1.48 kJ/mm is used for preheating welding at 75 ℃.This is because preheating reduces the cooling rate of the low temperature zone of the welded joint, improves the microstructure of the coarse grain zone, and improves the cold crack resistance.When the line energy of 3.08 kJ/mm is used for welding, the critical fracture stress is 870 MPa without preheating and 850 MPa with preheating at 75℃.The coarse grain zone in the heat affected zone is a mixture of martensite and bainite.The embrittlement of the coarse grain zone is low, which improves the cold crack resistance to some extent.However, due to large line energy, especially under preheating, the softening degree of the softening zone in the heat affected zone is increased, the critical fracture stress of the welded joint is reduced.