MicroRNAs (miRNAs) play pivotal roles in the formation and progression of breast cancer (BC). Here, we attempt to identify miRNAs associated with BC prognosis and progression through integrated analysis. We firstly screened out 83 differentially expressed miRNAs (DEMs) in 1249 BC samples and 151 normal samples. Then, we validated their roles in expression and prognosis, identified 2 survival-related DEMs, and established a risk model. The prediction efficiency was assessed both in the training group and the validation group. ROC curve indicated a good prediction ability with 1, 3, and 5 years survival of 0.73, 0.72, and 0.72, respectively. Moreover, hsa-miR-127 was found as an independent prognostic factor for BC. Functional analyses revealed it is involved in various cancer pathways, such as the PI3K-Akt pathway and p53 pathway. Additionally, tissue and cell experiments were conducted to verify the regulatory effect of miR-127 in BC. The expression of miR-127 was down-regulated both in BC tissue and cell lines. The interference or overexpression of miR-127 was significantly increased or decreased BC cell proliferation, invasion, and migration, respectively. And this effect of miR-127 was consistent with tumorigenic ability and tumor volume in nude mice. These findings indicated that low expression of miR-127 contributes to BC migration, invasion, and tumorigenesis, and suggested a therapeutic target and prognostic biomarker for BC.