Abstract: Objective The aim is to analyze the influence of microstructure on the longitudinal section hardness of rail flash butt welding joints. Methods The characteristic parameters such as hardness, microstructure, pearlitic lamellar spacing, grain orientation and grain size in different micro-zones of European standard R260 grade pearlitic rail flash butt welded joints, which are characterized and studied, using the OEM, SEM and EBSD methods, and the influence of microstructure and grain characteristic parameters of different micro-zones of rail flash butt welded joints on the longitudinal section hardness of the joints are clarified. Results The results show that using the average value and the standard error value that can reflect the normal distribution characteristics of measurement errors are more accurate to represent the pearlitic lamellar spacing in specific material pearlitic rails, which is under certain process conditions. The influence of grain size on the longitudinal section hardness of the pearlitic rail flash butt welded joints is more significant than that of pearlitic lamellar spacing. Conclusion It provide theoretical basis for the composition design and welding process optimization of rails