Multiple Myeloma (MM) is a plasma cell myeloma. Long non-coding RNA (lncRNA) prostate cancer associated transcript 1 (PCAT1) has been identified as being associated with various types of cancer. However, the mechanism of PCAT1 was still undefined in MM. In the current study, PCAT1 and metadherin (MTDH) were up-regulated and miR-363-3p was down-regulated in MM bone marrow plasma and cells. Furthermore, PCAT1 knockdown inhibited cell proliferation, cell cycle progression, and the protein kinase B (AKT) and β-catenin signaling pathway, but induced cell apoptosis by regulating MTDH. PCAT1 was verified to sponge miR-363-3p, and MTDH was identified as a candidate target of miR-363-3p. Meanwhile, PCAT1 positively modulated MTDH expression by sponging miR-363-3p. In addition, PCAT1 knockdown blocked xenograft tumor growth in vivo. Thus, we concluded that PCAT1 facilitated cell growth in multiple myeloma by activating the AKT/β-catenin signaling pathway through the miR-363-3p/MTDH axis.