The phase transformation process of U-2Nb alloy under isothermal condition and the mechanical properties corresponding to the morphological changes were studied within 450℃~635℃.By applying the Optical Microscope、Scanning Electron Microscope techniques, tensile and compression tests, the relationship between structure and performance was discussed. The results show that U-2Nb alloy has two distinct microstructure features during isothermal heat treatment from 550℃ to 635℃. The main factor affecting the strength and plasticity was the lamellar spacing of the dual-phase in the range of 550℃~635℃.The lamellar spacing was mainly determined by the formation temperature. The higher the temperature, the greater the lamellar spacing, and so, the lower the strength and the higher the plasticity. The isothermal time is positively correlated to the lamellar spacing. The best overall properties we obtained were elongation of 22%, reduction area of 27.4%, tensile strength of 875Mpa and yield strength of 410Mpa.The rest samples were quenched and annealed at 450℃~500℃.The main factors influencing the mechanical properties within this temperature range are speculated to be the texture of the acicular martensite and the distribution or size of the granular structure. All samples with quenching+annealing treatment show overall strength higher than 1000Mpa, but with low plasticity. Elongation and reduction of area were within 5%. The annealing temperature affect the strength much more than plasticity. The plasticity was improved slightly by extending the annealing time.