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Hypoxia‐induced cardiac fibrosis is an important pathological process in cardiovascular disorders. This study aimed to determine whether low‐intensity pulsed ultrasound (LIPUS), a novel and safe apparatus, could alleviate hypoxia‐induced cardiac fibrosis, and to elucidate the underlying mechanisms. Hypoxia (1% O2) and transverse aortic constriction (TAC) were performed on neonatal rat cardiac fibroblasts and mice to induce cardiac fibrosis, respectively. LIPUS irradiation was applied for 20 minutes every 6 hours for a total of 2 times in vitro, and every 2 days from 1 week before surgery to 4 weeks after surgery in vivo. We found that LIPUS dose‐dependently attenuated hypoxia‐induced cardiac fibroblast phenotypic conversion in vitro, and ameliorated TAC‐induced cardiac fibrosis in vivo. Hypoxia significantly upregulated the nuclear protein expression of hypoxia‐inducible factor‐1α (HIF‐1α) and DNA methyltransferase 3a (DNMT3a). LIPUS pre‐treatment reversed the elevated expression of HIF‐1α, and DNMT3a. Further experiments revealed that HIF‐1α stabilizer dimethyloxalylglycine (DMOG) hindered the anti‐fibrotic effect of LIPUS, and hampered LIPUS‐mediated downregulation of DNMT3a. DNMT3a small interfering RNA (siRNA) prevented hypoxia‐induced cardiac fibrosis. Results also showed that the mechanosensitive protein‐TWIK‐related arachidonic acid‐activated K+ channel (TRAAK) messenger RNA (mRNA) expression was downregulated in hypoxia‐induced cardiac fibroblasts, and TAC‐induced hearts. TRAAK siRNA impeded LIPUS‐mediated anti‐fibrotic effect and downregulation of HIF‐1α and DNMT3a. Above results indicated that LIPUS could prevent prolonged hypoxia‐induced cardiac fibrosis through TRAAK‐mediated HIF‐1α/DNMT3a signalling pathway. [ABSTRACT FROM AUTHOR]