The invention relates to a high-resilience polyurethane elastic fiber which is formed by the copolymerization of oligo-diatomic alcohol, diisocyanate and chain extender segment and a preparation method thereof; the invention is characterized in that: prepolymerization is conducted in a solvent, the oligo-diatomic alcohol with different molecular weights are used and a certain quantity of content of polymer end group is controlled to obtain the property of the high-resilience polyurethane elastic fiber. The polyurethane elastic fiber prepared has excellent resilience and breaking elongation rate.