Abstract: Objective This article focuses on cold cracking sensitivity of domestically produced 1 000 MPa high-strength steel (HSS) for hydropower applications. Methods Theoretical calculations of preheating temperature were conducted with carbon equivalent, plate thickness, diffusion hydrogen content of deposited metal, and welding heat input as influencing factors. The preheating temperature for backing welding was determined through TEKKEN test. The critical fracture stress at different preheating temperatures was determined through implant test. Results The results show that theoretical preheating temperature of steel plate is 133 ℃. Preheating temperature for backing welding with a heat input of 7.4 kJ/cm should not be lower than 125 ℃. Under no preheating conditions, critical fracture stress of steel plate is 550 MPa. When preheated to 80 ℃, critical fracture stress of steel plate is 850 MPa. When preheating temperature exceeds 100 ℃, critical fracture stress of steel plate is 1 025 MPa. Conclusion 1 000 MPa high-strength steel with a thickness of 80 mm for hydropower has a certain tendency towards cold cracking. Based on practical engineering applications, it is recommended to preheat at least 125 ℃ before welding, and interpass temperature should not be lower than 125 ℃ to avoid cold cracking at the root and heat affected zone.