Abstract: The optical microscopy, SEM-EDS, EBSD and other detection and characterization methods were used to characterize and analyze the abnormal "black fleck" microstructure during the hot rolling process of TC1 alloy sheet.Moreover, the mechanical properties of the "black fleck" microstructure and normal matrix were also compared. The results show that there is no segregation phenomenon in these areas, whose average Vickers hardness is 23 HV higher than that of the normal matrix area. The essence of the "black fleck" microstructure is the fine non-recrystallized sub-crystalline grains with small angle grain boundaries, they are formed in the rolling deformation process. Increasing heat treatment temperature and extending holding time have no significant effects on the abnormal "black fleck" microstructure. In addition, there is no significant difference between the mechanical properties of abnormal "black fleck" microstruture and normal matrix microstruture at room temperature and 400℃.