The invention discloses a synbiotic feed additive for growing and fattening of pigs. The synbiotic feed additive is prepared from composite probiotic agents, maltodextrin, isomaltooligosacharide, glucose, citric acid, composite vitamins, composite trace elements, charcoal, attapulgite, leguminosae, dioscorea opposita, poria cocos, atractylodes macrocephala rhizomes, dried unripe fruits of citrus aurantium, common vladimiria roots, Chinese thorowax, dried ripe fruits of crataegus pinnatifida, oblongleaf kadsura stems or roots and bidens pilosa. The invention further provides an application method of the additive. During the growth and fattening period of pigs, the synbiotic feed additive for growing and fattening of pigs is added to a feed according to the addition quantity of the synbioticfeed additive to the body weight of fattening pigs being 0.1-5% for feeding. Through adoption of the synbiotic feed additive for growing and fattening pigs and the application method disclosed by theinvention, the weight increment speed of the body weight of the pigs can be increased, the lean meat proportion is increased, the nutrients are comprehensive, the feed feeding quantity can be reduced, the utilization rate of the feed can be increased, the growth speed of the pigs is high, the meat quality is bright red, tender in nature and good in mouth feel, the economic benefits are increased,and the synbiotic feed additive has good application prospects.