Fibroblast-to-myofibroblast differentiation is the main cytopathologic characteristic of pulmonary fibrosis. However, its underlying molecular mechanism remains poorly understood. This study elucidated that the nuclear export of lncNONMMUT062668.2 (lnc668) exacerbated pulmonary fibrosis by activating fibroblast-to-myofibroblast differentiation. Mechanistic research revealed that histone H3K9 lactylation in the promoter region of the N6-methyladenosine (mA) writer METTL3 was enriched to enhance METTL3 transcription, leading to the lnc668 mA modification. Meanwhile, the mA reader YTHDC1 recognized mA-modified lnc668 and elevated the METTL3-mediated lnc668 modification. Subsequently, phase-separating YTHDC1 promoted the nuclear export of mA-modified lnc668. In this process, the phase-separating YTHDC1 formed a nuclear pore complex with serine/arginine-rich splicing factor 3, Aly/REF export factor, and exportin-5 to assist the translocation of mA-modified lnc668 from nucleus to cytoplasm. After nuclear export, lnc668 facilitated the translation and stability of its host gene phosphatidylinositol-binding clathrin assembly protein to activate fibroblast-to-myofibroblast differentiation, leading to the aggravation of pulmonary fibrosis, which also depended on YTHDC1 phase separation. This study first clarified that YTHDC1 phase separation is crucial for the mA modification, nuclear export, and profibrotic role of lnc668 in exacerbating pulmonary fibrosis. These findings provide new insights into the nuclear export of cytoplasmic lncRNAs and identified potential targets for pulmonary fibrosis therapy.