The invention relates to a welding method of a boiler economizer. The economizer is an important component of a heating assisting surface in a coal fired boiler and can bear relatively large temperature and pressure during use; the manufacturing quality greatly influences the running and normality of the boiler; when in manufacturing, the welding quality is the important index for evaluating the manufacturing quality and the manufacturing process level; good welding process can prolong the service life of the economizer. An inner hole welding method of the boiler economizer comprises the steps of 1, preparing for welding; 2, performing spot welding; 3, performing backing welding; 4, welding a surface covering layer. The method is applied to inner hole welding of the boiler economizer.