Brain metastases are the most common intracranial malignancies, and radiotherapy is an effective treatment of controlling the localized lesions. However, conventional radiotherapy techniques have their own shortcomings that limit the effectiveness of radiotherapy. Metastatic brain tumors are highly likely to recur or progress after treatment. Clinical studies have shown that arginine can penetrate the blood-brain barrier and subsequently improve the radiosensitization of metastatic brain tumors. In this article, the mechanisms underlying the effect of arginine on the radiosensitization of metastatic brain tumors by inhibition of tumor glycolytic metabolism, reduction of DNA damage repair and alteration of tumor hemodynamic parameters were reviewed, aiming to provide new ideas for clinical research and treatment of brain metastases.