Three-dimensional small crack propagation behavior of deforming TiAl alloy at 650℃ is studied by in-situ observation fatigue testing, and then long crack propagation behavior of the alloy in temperature range from 650℃ to 800℃ is studied by fatigue crack propagation tests. It shows that, the three-dimensional small cracks can still grow even though in the stress intensity factor region that below the long crack propagation threshold value, furthermore, the growth rates of small cracks are higher than long cracks in this region; The sample edge straight horizontal manufacturing nick is one of the main positions of three-dimensional small crack initiation of the alloy. Small cracks merge at the position of bends that occur during the fatigue testing. The fatigue life of the alloy is not sensitive to irregular strip manufacturing defects on the surface of the sample; The steady propagation rates of long fatigue cracks of the alloy are not sensitive to temperature changes in temperature range from 650℃ to 800℃. All the long crack propagation processes exhibit the cleavage fracture. Crack propagation threshold values are related to ductile-brittle transition temperature, the temperatures below the ductile-brittle transition temperature have lower threshold values.