TiAl-based alloys appear as potential competitors to steels and superalloys applied in aerospace and automotive industries due to their low density, high specific strength and stiffness and good oxidation resistance at elevated temperatures. As a new generation of TiAl-based alloys, high Nb-containing TiAl alloys have become a promising high temperature structural material due to their better high temperature strength and oxidation resistance than ordinary TiAl alloys. TiAl-based alloy components such as low pressure turbine blade and compressor impeller often serve in near steady conditions for a duration of time once peak operating conditions are achieved at high temperature. The components suffer not only from rapidly induced damage from start-up and shutdown cycles, but also from creep damage under sustained loading periods. Moreover, the possible interaction damage between fatigue and creep must be considered. Thus, the study of fatigue-creep interaction for TiAl-based alloys is of great practical importance. Large numbers of researches were focused on the fatigue or creep properties of TiAl-based alloys, however, the fatigue-creep interaction behavior was rarely reported. Therefore, the crack initiation and propagation behavior of a nearly lamellar Ti-45Al-8Nb-0.2W-0.2B-0.1Y alloy in fatigue-creep interaction was observed at 750 ℃. The cyclic loading tests were carried out using a mini servo-hydraulic fatigue machine in a SEM chamber. The entire process of crack initiation and propagation was observed. The load cycling was trapezoidal by applying a dwell time at the maximum tension stress. The results indicated that micro-cracks mainly occurred at internal grain boundaries in the form of creep void or fatigue micro-crack. The micro-cracks firstly extended along the grain boundary by absorbing the creep voids or the stress concentration around crack tips, then connected with each other forming a longer crack. As the crack was frustrated by grain boundaries of other orientations, the crack began to grow in the thickness direction. Meanwhile, the micro-cracks perpendicular to loading direction emerged. Eventually, the frustrated cracks interconnected resulting in fracture. Compared to the in situ SEM observations in fatigue deformation, the dwell time resulted in the increase of probability of grain boundary crack initiation and the changes of crack propagation path. Thus, the fracture mode transform from transcrystalline to intercrystalline and the fatigue lifetime significantly decreased. The model of the crack initiation and propagation behaviors of high Nb-containing TiAl alloys in fatigue-creep interaction was presented in this work.