Abstract: The critical rapture stresses and the welding thermal cycling parameters of implant test were measured under 4 welding conditions,and the fracture morphology were observed. The cold cracking susceptibility of 10Ni8CrMoV was studied and a formula of the critical stress and hot-cycle parameters(t_8/5,t₁₀₀) was calculated on the basis of t_8/5,t₁₀₀ and the critical fracture stress. The results indicated that raising the preheating temperature and the postheating cauld decrease the cracking susceptibility of 10Ni8CrMoV,but would enchance the hardness of HAZ.Resultsfrom the prediction formular for the critical stress showed agreement with the results from Tekken test.