The phase transition rule of near-β Ti-3Zr-Mo-15Nb (TLE) medical titanium alloys was analyzed through DSC curves and XRD patterns; effects of the processing and the heat treatment on microstructure and mechanical properties of the TLE alloys was investigated by OM, TEM and tensile experiments. The results show that fine and equiaxed grains in the TLE alloy are formed after rolling in the (α+β) phase field and solution-treatment; quenching of the β phase filed results in the formation of a metastable martensitic structure α" (orthorhombic). After low-temperature aging, some of α" martensite is decomposed into α martensite; with the aging temperature increasing, α" martensite is absolutely decomposed into α martensite. When the aging temperature is 250 oC, high strength, low modulus and high plasticity of the alloy can match preferably with human bone. The microstructure observation of the alloy indicates that the interaction between a few α" orthorhombic martensite, α martensite and certain dislocation lead to lower elastic modulus and higher plasticity, while a lot of cross martensite which are fine and needle-like contribute greatly to biomechanical property.