The pre-weaned weight gain is an important performance trait of pigs in intensive pig production. The bacterial microbiome inside the host is vital to host health and growth performance. The purpose of this study was to explore the possible associations of the intestinal microbiome with the pre-weaned weight gain in intensive pig production. In this study, several anatomical sites (jejunum, ileum, cecum, and colon) were examined for bacterial microbiome structure using 16S rRNA V4-V5 region sequencing with Illumina Miseq. The results showed that the microbial richness (estimated by Chao1 index) in jejunum was positively correlated with the pre-weaned weight gain. This study also revealed that the Firmicutes and Bacteroidetes in colon were the weight gaining-related phyla; while the Selenomonas and Moraxella in ileum and the Lactobacillus in both cecum and colon were the weight gaining-related genera for the pre-weaned piglets in intensive pig prodution. Several intra-microbial interactions within commensal microbiome correlated with the pre-weaned weight gain were excavated, as well. Overall, this study provides an expanded view of the commensal bacterial community inside four anatomical intestinal sites of the commercial piglets and the associations of the intestinal microbiome with the pre-weaned weight gaining performance in intensive pig production.