The superficial temporal artery and vein has always been the donor vein for free flap to repair the upper 2/3 defects of the face. This paper reports a case of free forearm flap repair after resection of frontal malignant tumor. During the operation, it was found that the superficial temporal vein was too small to meet the requirements of donor vein, and the posterior mandibular vein was used as donor vein, and the flap survived after operation.