Objective To explore the cause of hoarseness of voice in patients after thyroidectomy with recurrent laryngeal nerve exposure. Methods The patients from January 2019 to December 2020 underwent thyroidectomy with exposure of recurrent laryngeal nerve during operation were selected. There were 19 cases of hoarseness of voice after operation followed up for 12 months. Postoperative observations included the characteristics of the hoarseness of voice, duration, and direct laryngoscope neck ultrasonography. Results A total of 19 patients had voice hoarseness, only 5 of them had recurrent laryngeal nerve injury during operation, the other 14 patients had good exposure and protection of recurrent laryngeal nerve. Direct laryngoscope showed that 4 of 14 patients had vocal cord edema and 1 had subluxation of arytenoid cartilage. About 1 week after operation, ultrasound examination showed that 11 of 14 patients had varying degrees hydrops of wound cavity. Conclusions Although the routine exposure of recurrent laryngeal nerve reduces the incidence of postoperative hoarseness of voice, the injury of recurrent laryngeal nerve is still a cause of postoperative hoarseness of voice. In addition, non-operative direct factors, such as fluid accumulation in the operative field, vocal cord injury caused by anesthetic intubation and other intubation related complications, are also important reasons for postoperative hoarseness of voice in these patients, which we should pay more attention to.