This prospective study aimed to investigate metastases of oral squamous cell carcinoma (OSCC) to cervical lymph nodes and submandibular glands and to analyze the safety and feasibility of preserving and using submandibular glandular flaps to repair postoperative OSCC defects.Overall, 330 patients with OSCC who met the inclusion criteria were enrolled in the study from January 2014 to July 2018. OSCC metastasis to cervical lymph nodes and submandibular glands was investigated using intraoperative frozen section and postoperative pathological observation. Fifteen patients who underwent repair of postoperative OSCC defects with submandibular glandular flaps were monitored for postoperative wound healing, complications, pathology, and appearance satisfaction and were followed up long term.Among the 330 patients with OSCC, the most common type was tongue cancer (138/330); 204 patients were node negative and 126 were node positive. Of 363 samples of the submandibular gland, 7 were metastatic with stage IV lesion, 5 were directly invaded by the primary tumor, and 2 were metastatic with extranodal extension in level Ib. None of the submandibular gland samples showed intraglandular hematogenous and nodal metastases. The repair of OSCC defects with submandibular glandular flaps was successful in all 15 patients, including 11 males and 4 females, with an age range of 19-74 years and a mean of 51 years. Of 15 patients, some had complications with heart and cerebrovascular diseases, diabetes, or chronic respiratory disease. All the submandibular glandular flaps survived postoperatively without any complications, and the mucosification on the surface was adequate. Follow-ups (median duration: 14 months) revealed the satisfactory recovery of shape and function without any local recurrences or distant metastases.Direct invasion is the main form of OSCC metastasis to the submandibular gland, while hematogenous and nodal metastases are uncommon. Preservation of the submandibular gland is oncologically safe. Thus, repair of postoperative OSCC defects with submandibular gland flaps is a feasible and promising procedure.Abbreviations: DIPT = direct invasion of primary tumors, IGLN = intraglandular lymph node, OSCC = Oral squamous cell carcinoma, PGLN = periglandular lymph nodes.