Abstract: Objective Welding heat input is an important factor affecting welding thermal cycle, fatigue fracture is one of the main failure forms of welding structure, fatigue crack growth rate (da/dN) is the characteristic parameter to characterize the speed of crack growth. The influence of different welding heat input on fatigue crack growth of B780CF steel welded joints was studied and analyzed by intuitive analysis method and statistical analysis method. Methods Submerged arc automatic welding was used to weld B780CF steel under four welding heat inputs, metallographic tests were carried out weld zone to analyze microstructure of welded joints, and multi-sample fatigue crack growth experiments were carried out, fatigue crack growth rate da/dN was calculated by seven-point increment term, stress intensity factor range ΔK was calculated, and the parameters in the fatigue crack growth rate equation based on Paris’ formula were obtained by least squares fitting. Results The results of visual analysis and statistical analysis show that the welding heat input has a significant effect on the fatigue crack growth of B780CF steel, and the greater the heat input, the greater the fatigue crack growth rate. The analysis of the results of metallographic test and fatigue crack growth test shows that fatigue crack growth is related to microstructure of weld zone, and the larger the welding heat input, the larger the grain of microstructure of weld zone, and the faster the fatigue crack propagation. Conclusion Excessive welding heat input should be avoided during welding to ensure the life of the welded structure, it is recommended to take a medium heat input when welding.