The present invention discloses a nonlinear fitting method for a cooling process of a polymeric phase change material. The method comprises the following steps of: (1) taking the polymeric phase change material as a to-be-tested sample, heating the to-be-tested sample to an initial temperature T1, holding the temperature until the to-be-tested sample is completely melted, then rapidly transferring the to-be-tested sample into a cooling medium of which the temperature is T2, inserting a T-shaped thermocouple into the melted to-be-tested sample at the same time, and acquiring temperature variation values of the to-be-tested sample in the whole cooling process; (2) according to temperature and time data acquired in the step (1), drawing a cooling curve; (3) performing dimensionless processing on the cooling curve, and setting a dimensionless temperature theta to be equal to the value of (T-T2) / (T1-T2); and (4) according to the theta value obtained in the step (3), performing nonlinear fitting by means of the following algorithm: y=(A+B) / (C+ex-D)-B, and making x equal to ln t and y equal to theta, so that a nonlinear fitting parameter in the cooling process of the polymeric phase change material can be obtained. A four-parameter model formula fitting method proposed by the present invention is convenient, has very good fitting effects for different polymeric phase change materials, and is higher in fitting accuracy.