The invention relates to a nano-composite phase change energy storage material with long cycle life and a preparation method thereof. The preparation method includes the following steps that 1, sodium acetate trihydrate is heated to be completely melted, a nano dispersing agent, a viscosity modifier and a nucleating agent are added, the materials are stirred, and a multi-phase non-uniform colloid dispersion system is obtained; 2, a water binding agent is added into soft water, ultrasonic treatment is carried out till the water binding agent absorbs water to be saturated, and a mixture is obtained; 3, the mixture is added into the multi-phase non-uniform colloid dispersion system, the materials are subjected to a stirring reaction for 60-90 min at the temperature of 70-100 DEG C, cooling crystallization is carried out, and the nano-composite phase change energy storage material with the long cycle life is obtained. The nano-composite phase change energy storage material is long in cycle life, stable in phase change temperature and good in heat stability, the phase change temperature is 50-58 DEG C, the phase change latent heat is 200-230 kJ/kg, and the nano-composite phase change energy storage material has reliable phase change crystallization stability. The preparation method of the nano-composite phase change energy storage material is simple, and the cost is low.