In order to investigate the fatigue behavior and fatigue life prediction method of butt weld on cast steel joint, a series of fatigue tests were conducted on welded specimens of cast steel and hot rolled steel with a common welding type. Relationships between stiffness, displacement and fatigue life stage were obtained. Fatigue failure mechanism was revealed based on the phenomenon of fatigue process and fracture surface observation resulted by scanning electron microscope (SEM). In addition, fatigue life prediction was carried out with effective notch stress method (ENSM). In consideration of the influence of mean stress and residual stress, improved effective notch stress method (IENSM) was proposed, and the predicted values were compared with the test data. The result shows that:The fatigue process of butt weld on cast steel joint can be divided into two stages:stable stage and fracture stage. The stable stage possesses more than 80% fatigue life, while the fracture stage maintains less than 20%. ENSM can predict the changing trends of the fatigue life to some extent, but the results are non-conservative for engineering. However, IENSM can provide safe assessments.