The invention discloses a method for improving high-temperature heat stabilization of thermoplastic polymers or composites thereof by alkyl metal phosphite. The method includes adding the alkyl metalphosphite into a raw material, wherein the adding amount of the alkyl metal phosphite accounts for 0.1-2% of the total weight of the thermoplastic polymers or the composites thereof, the structural formula of the alkyl metal phosphite is shown as the following formula (I) or the following formula (II), R is selected from an aryl group or a linear-chain aliphatic alkyl group with the carbon numberof 1-6, and Me is selected from zinc, calcium or magnesium. The method has the advantages that cross-linking, decomposition, degradation, discoloration and other problems of the thermoplastic polymersor the composites thereof are avoided under the joint action of the high temperature and the shearing force, and various properties of the materials are maintained.