Early life intervention is important to shape the gut microbiome profiles of adult animals due to the tremendous alteration of diet components. Nevertheless, there is still no unified understanding about its long-term effects in lambs. In this study, sixty 20-day-old lambs were assigned into ewe-rearing (ER) and artificial-rearing (AR) treatments to evaluate the effects of AR strategy on ruminal microbiota, fermentation, and morphology of pre-weaning lambs (from 20 to 60 days of age) and its long-term effects in the fattening stage (from 61 to 180 days of age). During the pre-weaning stage, ER lambs were breastfed and supplemented starter, while AR lambs were artificially fed with milk replacer and starter. During the fattening stage, all lambs in both treatments were fed with the same fattening diets. At 60, 120 and 180 days of age, 6 lambs from each group were slaughtered to collect rumen content and tissue samples. Compared with ER lambs, the dry matter feed intakes of AR lambs increased (P<0.05) from 20 to 180 days of age, companying an increased average daily gain (ADG) from 61 to 120 days of age (P<0.05) and from 121 to 180 days of age (0.050.05), it was higher (P<0.05) in AR lambs compared with ER lambs at the fattening stage. The rumen keratin layer of AR lambs was thinner (P<0.05) than that of ER lambs. Along with lamb growth from 60 to 180 days of age, the differences in rumen bacterial diversity between AR and ER treatments grew more distinct (P<0.05). Compared with ER lambs, AR lambs increased (P<0.05) rumen bacteria abundance, such as phylum Spirochaetes and genus Treponema at 60 days of age, phylum Actinobacteria and genus Succiniclasticum at 120 days of age, and phylum Proteobacteria at 180 days of age, but decreased genus Selenomonas from 60 to 180 days of age, and Anaerovibrio at 180 days of age. In summary, the early interventions before weaning could improve dry matter feed intake of lambs, which triggered robust rumen development and produced positive long-term effects on rumen fermentation and noticeable weight gain of fattening lambs. It suggests that the artificial rearing strategy is effective in improving rumen fermentation and microbial maturity of intensive fattening lambs.