The near isothermal canned hot extrusion at a temperature close to α transus temperature was used to fabricate Ti－45.5Al－2Cr－2Nb－0.15B alloy rod. Microstructures and tensile properties of samples taken from different locations of the extrudate were compared with each other, and the formation mechanism of extrusion microstructure was investigated in combination with the finite element simulation. It was found that lamellar grains were significantly refined by hot extrusion. Microstructure and tensile elongation were homogeneous along the axial direction of extruded rods, but heterogeneous along the radial direction. The center of rods with coarse fully－lamellar microstructure had low tensile elongation, and the edge of rods with fine near lamellar microstructure had high tensile elongation. Such heterogeneities could not be eliminated in subsequent α solid solution treatment. Lamellar grain size decreased with increasing effective strain. There existed the refined homogeneous microstructure in the regions with effective strain larger than 2.25. The difference of microstructure type was mainly due to different temperatures of different parts of rods during extrusion process. In the edge of rod tails, the γ phase lamellar structure precipitated from α phase was formed due to the chilling effect caused by contacting with the cold die, then the lamellar structure with tortuous boundary was formed in subsequent deformation. Tensile elongation was found to decrease with increasing lamellar grain size, but the poor tensile elongation in the center was mainly attributed to the existence of lamellar grains which lamellar boundaries were nearly perpendicular to the extrusion direction.