Abstract: Aiming at the engineering problems of high cold cracking susceptibility of 25 mm thick Q690 high strength steel plate and increased manufacturing cost caused by excessive preheating temperature before welding, the weldability under low preheating conditions was investigated based on empirical formulas and theoretical analysis. The Tekken test and implant test were adopted to evaluate the cold cracking susceptibility of the steel plate. Combined with the simulated heat affected zone continuous cooling transformation (SH-CCT) characteristics, gas metal arc welding (GMAW) butt welding procedure qualification was carried out, and the microstructure and mechanical properties of the welded joints were systematically characterized. The theoretically calculated minimum preheating temperature for preventing cold cracks of the steel plate is 34 ℃-35 ℃. No cold cracks were observed in the Tekken test at 35 ℃. The critical fracture stress obtained from the implant test is no less than 875 MPa, which is markedly higher than the yield strength of the base metal. Non destructive testing reveals no welding defects in the low preheating butt welded joint. Indicators including tensile strength, side bend performance, impact toughness at -20 ℃ and hardness of the welded joint all meet the standard service requirements. The thermal cycles during multi pass welding can achieve significant grain refinement in the coarse grained heat affected zone. The research demonstrates that the 25 mm thick thermomechanical control processed Q690 high strength steel plate is feasible for welding under low preheating condition (35 ℃).