The present invention discloses an additive for polymer, and the additive for polymer comprises: A: a phosphinate comprising two substituent groups, which has following structural formula (I), wherein R 1 and R 2 are the same or different, which represent H, C1-C6-alkyl or C6-C18-aryl; M is Al; m is 3; and B: a metal element of calcium, wherein a mass content of the metal element of calcium in a total additive is 10 to 600 ppm. According to the present invention, the additive that contains a specific range of content of the metal element of calcium has a simple preparation process and a low production cost, by using the additive in the polymer, a fatigue resistance of a product of a polymer composition can be greatly improved and a high-efficient fire retarding performance of the polymer composition can be guaranteed at the same time.