Abstract: With welding heat-cycle system,the temperature signal of root layer at welded joint of 10CrMo910 heat resistant steel was collected under the two different welding input.Through comparing curve and parameters of welding thermal cycle under the condition of two different heat input,the effect of heat input on thermal cycle of root layer for 10CrMo910 heat resistant teel was discussed together with observation of microstructure and hardness testing.The results showed that heat input of 10CrMo910 heat resistant steel had great impact on thermal cycle,the parameters of thermal cycle such as peak temperature and t_8/3 are low under low heat input,the microstructure at room temperature was finer and hardness values was higher;the higher the higher heat input,the microstructure at room temperature was coarser and hardness values was lower.