The invention provides a processing agent for polyolefin and alloy thereof, comprising the following blended components: oligomer and polyprotic acid, wherein the molar ratio of the oligomer to the polyprotic acid is from 1:0.1 to 1:10; the oligomer is linear or short branched chain oligomer, of which the molecular weight is from 2000 to 20000, and two ends or one end of the oligomer is provided with polar end groups or a polar end group; and the polyprotic acid is organic polyprotic acid or inorganic polyprotic acid. The processing agent has the advantages of small volume of addition, short effective time, favorable viscosity effect and the like when used in the polyolefin and the alloy thereof. By adopting an acid modifying method of acid modification, the heat resistance of the oligomer is improved so that the decomposition problem is not existed under the normal processing temperature and the product can not fade.