The relationship of processing-structure-property for the orthorhombic phase based alloy, Ti-22Al-20Nb-7Ta (at%), developed recently in CISRI was evaluated. Three typical microstructures, lath, equiaxed and duplex, were obtained by different theremo-mechanic processing (TMP) techniques, The duplex microstructure has an optimum: combination of tensile yield strength and ductility both at room and elevated temperatures. Comparing with Ti-22Al-27Nb alloy, adding Ta to partially replace Nb in Ti-Al-Nb orthorhombic alloys can improve the yield strength especially at high temperature while retain good room ductility. TEM examination on the tensile deformation dislocation structure of the equiaxed (O+B2) microstructure showed that the,,motion of a large amount of <112> and <114> dislocations of c+a/2 type on the slip planes of {211} and {041} occurred. The c+a/2 type super-dislocation dissociation of 1/2[114] in O phase was also recognized. The initiation and propagation of cracks for the equiaxed and duplex microstructures during SEM in-situ tensile process were also examined.