The composition of bacteria in the gastrointestinal tract of piglets is easily affected by environmental changes, particularly during the weaning period. Compound strains ofLactobacillus reuteriandLactobacillus salivariuswere supplemented to piglets during pre- and post-weaning to determine their effects in improving the growth performance and ameliorating the diarrhea rate and stress caused by antioxidation in piglets. A larger number ofL. reuteriandL. salivariuscolonized the distal segment of the ileum and the total numbers ofLactobacillusspp.andBifidobacteriawere higher in the ileal mucous membrane and cecal lumen with probiotics supplementation. The numbers of antioxidants and immune molecules increased, levels of cortisol and endotoxin reduced, and growth hormone and insulin-like growth factor 1 improved in the plasma following compound bacteria (CL) supplementation. Spearman's and KEGG analysis of the bacterial operational taxonomic unit and antioxidative and immune indices and metabolic genes indicated that the body growth modulation by CL supplementation could be attributed to optimization of the intestinal bacterial composition; functional strains ofL. delbrueckii,L. salivarius,L. formicilis,L. reuteri, andL. mucosaewere positively correlated with body antioxidation and immunity derived by CL supplementation. Strains ofL. agilisandL. pontiswere diverse and negatively correlated with body antioxidation and immunity. Collectively, these results suggest that supplementation with CL could reduce stress and improve the growth performance of piglets during weaning by optimizing the intestinal bacterial composition.