Objective: To investigate the causes of thermal injury of recurrent laryngeal nerve (RLN) and the preservation methods. Methods: Between June 2009 to December 2011, 513 patients scheduled for thyroid surgery in Shaanxi Provincial People’s Hospital were randomly divided into two groups for prospective study. Of the patients, 247 cases received preventive treatment for thermal injury of the RLN (observational group) and 266 cases received no preventive treatment (control group) during operation. The surgical management comprised unilateral subtotal thyroidectomy in 205 cases, bilateral subtotal thyroidectomy in 155 cases, unilateral total thyroidectomy in 103 cases, and functional radical neck dissection for thyroid cancer in 50 cases. Results: Follow-up of the patients was conducted for 2 to 30 months, with an average of (25.6±3.2) months for observational group and (22.4±4.4) months for control group. Two-hundred and twenty-five (91.09%) patients in observational group and 248 (93.23%) patients in control group were followed up. RLN injury occurred in 13 patients (2.75%) in the entire group of patients, with 2 (0.89%) cases in observational group and 11 (4.44%) cases in control group which had statistical difference (P<0.05); of the 13 patients, 2 cases of permanent RLN injury were all in control group. Conclusion: Improper use of electric scalpel and ultrasound knife may cause thermal injury of the RLN, which is difficult to repair. Taking effective preventive and protective measures can reduce the incidence of thermal injury of the RLN.