The microstructure of high Nb-TiAl alloys was optimized by the addition of a small amount of Ta elements to further improve their properties. A series of Ti46Al1.5Cr8Nb-xTa (x=0.2, 0.4, 0.6, 0.8, 1.0, at.%) alloys were prepared by vacuum arc melting. The microstructure, mechanical properties, and related influencing mechanisms were systematically investigated. The results indicate that the solidification microstructure of the Ti46Al1.5Cr8Nb-xTa alloys comprises the γ-TiAl phase, α2-Ti₃Al phase, and B2 phase. As the Ta content increases from 0.2at.% to 1.0at.%, the content of α2 phase and B2 phase increases, while the γ phase content decreases. Among them, the B2 phase shows the most pronounced change, being significantly refined, with its content increasing from 12.49% to 21.91%. In addition, the average size of the lamellar colony decreases from 160.65 to 94.44 μm. The addition of the Ta element shifts the solidification path toward lower aluminum concentrations, leading to changes in phase content. The tantalum-induced increase in the B2 phase and enhanced supercooling at the solidification front provide the basis for lamellar colony refinement. Compressive testing at room temperature reveals that the Ti46Al1.5Cr8Nb0.4Ta alloy exhibits optimal compressive properties, achieving a compressive strength of 2,434 MPa and a compressive strain of 33.1%. The improvement of its properties is attributed to a combination of lamellar colony refinement, solid solution strengthening resulting from the incorporation of Ta element, and a reduction in the c/a of the γ phase.