Intrauterine adhesion (IUA), a major cause of uterine infertility, is pathologically characterized by endometrial fibrosis. Current treatments for IUA have poor efficacy with high recurrence rate, and restoring uterine functions is difficult. We aimed to determine the therapeutic efficacy of photobiomodulation (PBM) therapy on IUA and elucidate its underlying mechanisms. A rat IUA model was established via mechanical injury, and PBM was applied intrauterinely. The uterine structure and function were evaluated using ultrasonography, histology, and fertility tests. PBM therapy induced a thicker, more intact, and less fibrotic endometrium. PBM also partly recovered endometrial receptivity and fertility in IUA rats. A cellular fibrosis model was then established with human endometrial stromal cells (ESCs) cultured in the presence of TGF-β1. PBM alleviated TGF-β1-induced fibrosis and triggered cAMP/PKA/CREB signaling in ESCs. Pretreatment with the inhibitors targeting this pathway weakened PBM's protective efficacy in the IUA rats and ESCs. Therefore, we conclude that PBM improved endometrial fibrosis and fertility via activating cAMP/PKA/CREB signaling in IUA uterus. This study sheds more lights on the efficacy of PBM as a potential treatment for IUA.