The influence of dual phase microstructure on the fatigue mechanism of TiAl intermetallic alloy, coated with CoCrAlY alloy by the plasma spraying, was studied in vacuum at 1073 K from view point of mesocopic size which is several μm-1 mm size range. The crack growth was observed and photographed under high resolution conditions using elevated-temperature loading cyclic stage for the scanning electron microscope. The results revealed strong influences of coating layer and dual phase microstructure on the fatigue mechanism in the alloy. The main crack initiated from pores in coating layer. The main crack grew into TiAl substrate and meso-cracks initiated in TiAl substrate affected the crack growth behavior. Finally, the main crack linked with Meso-cracks. The fatigue property was dependent upon the mechanism retarding the main crack growth due to dual phase microstructure.