Objectives DM is characterized by skeletal muscle weakness and cutaneous manifestations. Plasma exosomes (EXOs) contain proteins, RNAs, DNA, and lipid cargoes and are transferred among cells. If thoroughly investigated, plasma EXO RNAs could potentially improve our understanding of DM pathogenesis. We aimed to identify potential new biomarkers and therapeutic targets for DM. Methods The RNA (mRNA, miRNA and lncRNA) profiles of plasma EXOs were evaluated by sequencing on the Illumina HiSeq 3000 platform. Differentially expressed (DE) RNAs and bioinformatic analyses were performed. Human skeletal muscle myoblasts cells (HSkMCs) were stimulated with plasma EXOs, rapamycin or IFN-beta. Real-time PCR and western blot analysis were used to detect related genes and proteins. Results A total of 689 DE mRNAs, 53 DE miRNAs and 452 DE lncRNAs were identified in DM plasma EXOs. Bioinformatic analysis inferred that plasma EXOs were secreted mainly by CD8+ T cells, regulatory T cells and natural killer cells. The DE miRNAs participated in the autophagy, TGF-beta and Wnt signalling pathways. Three DE miRNAs (hsa-miR-125a-3p, hsa-miR-1246 and hsa-miR-3614-5p) were correlated with serological indices, organ involvement and myositis-specific autoantibodies. The DE lncRNAs participated in autophagy, IFN-beta production and mTOR signalling. DM plasma EXOs can induce autophagy in HSkMCs by regulating three miRNAs (hsa-miR-125a-3p, hsa-miR-1246 and hsa-miR-3614-5p) and three lncRNAs (ENST00000584157.1, ENST00000523380.1 and ENST00000560054.1), which formed an autophagy network, playing a role in muscle damage. Conclusion Our study provides an overview of distinct RNA profiles in DM plasma EXOs, and verified some miRNAs as potential biomarkers and therapeutic targets. The findings provide important clues for more in-depth explorations of plasma EXOs in DM.