The invention relates to an energy-storage polyurethane fiber and a preparation method thereof. The energy-storage polyurethane fiber is composed of a wrapper and a core part, wherein the cross section of the fiber is solid, the core part accounts for 70-80% of the fiber by mass percent and the wrapper accounts for 20-30% of the fiber by mass percent; the preparation method of the polyurethane fiber comprises the following steps: 1. preparing a spinning solution of the core part of the energy-storage polyurethane fiber according to the proportion of the formula; 2. preparing a spinning solution of the wrapper of the energy-storage polyurethane fiber according to the proportion of the formula; and 3. operating by adopting dry spinning equipment and process to obtain the energy-storage polyurethane fiber. The polyurethane fiber has a function of adjusting the temperature of the human body, can absorb heat when the body temperature is raised, and can release the heat when the body temperature is reduced, and therefore, the wearing comfort level of the polyurethane fiber is improved; and besides, the polyurethane fiber has the excellent using performance and can meet the requirement of homespun on the spinning, weaving, dyeing and finishing processes.