Patients with diabetes mellitus combined with hypernatremia are mainly handled by hypoglycemic therapy and rehydration therapy, actively lowering glucose and limiting sodium intake to prevent excessive sodium input. The first step is to actively lower glucose, using oral hypoglycemic drugs or injectable insulin therapy to control blood glucose in a reasonable range. The patient is hydrated early with adequate amounts of water to correct the hypertonic state, followed by electrolyte supplementation as appropriate. Correction of hypernatremia should not be rushed; too rapid rehydration and reduction of the hypertonic state may trigger cerebral edema, convulsions, and neurologic damage, which can lead to death. Patients with diabetes mellitus combined with hypernatremia should not blindly take medication on their own.