The invention discloses a low-elastic-modulus high-strength titanium alloy and a preparation method thereof. The alloy comprises 18 at% of niobium, 0-9 at% of zirconium, 0-9 at% of hafnium and the balance of titanium, wherein the sum of the zirconium and hafnium is 0-9 at%. The preparation method comprises the following steps: smelting in a vacuum consumable/non-consumable arc-melting furnace to obtain a Ti-Nb-Zr(Hf) cast ingot, carrying out homogenizing treatment on the cast ingot, cogging, forging, carrying out intermediate forging, gradually cooling to 900 DEG C from 1000 DEG C to obtain an intermediate plate blank, carrying out solution treatment on the plate blank, and cooling to obtain a structure with orthorhombic martensite phase and residual beta-phase in a certain ratio; and carrying out cold-rolling until the amount of deformation is greater than 60%, thereby obtaining the low-elastic-modulus high-strength titanium alloy plate, of which the elastic modulus is 50-60 GPa, the rolling-direction tensile strength at room temperature exceeds 850 MPa and the elongation percentage is 6-15%. The alloy disclosed by the invention can be widely used in spectacle frames, sports equipment and biomedical devices.