To address the demand for lightweight high-temperature structural materials in the aerospace field (where Ti-Al-Nb alloys are promising candidates), this study prepared two Ti-Al-Nb alloys (Ti-15Al-24Nb and Ti-22Al-14Nb, at%) via elemental powder metallurgy, involving high-energy ball milling, cold isostatic pressing, and high-temperature sintering. The high-temperature compressive properties of the two alloys were tested under deformation conditions of 800–1100℃ (temperature range) and 1 × 10–2-10−1s−1 (strain rate range), and their constitutive equations were established based on the true stress-strain curves. Results show that the isothermally sintered Ti-Al-Nb alloys (prepared from elemental powders) are mainly composed of α2 and B2 phases. Both Ti-15Al-24Nb and Ti-22Al-14Nb alloys show decreasing peak stresses with rising temperature. At 0.1 s−1, their peak stresses are 490-75 MPa and 564-149 MPa respectively; at 1 × 10–2 s−1, the values are 430-44 MPa and 475-149 MPa respectively. Under the same deformation conditions, the peak stress of Ti-22Al-14Nb alloy is consistently higher than that of Ti-15Al-24Nb alloy. Further analysis of the true stress-strain curves of the two alloys led to the establishment of hyperbolic sine-type constitutive equations corresponding to their different phase regions.