Objective:Investigate the various factors affecting postoperative function of primary hyperthyroidism. Methods:80 patients with moderate and grave primary hyperthyroidism proven postoperatively and pathologically are selected and clinical data is documented.They are follow-up 1-8 years.The obtained data is analyzed by means of SAS software. Results:Age,sex,whether taking hyperthyroidism medicine,the course of disease and preoperative T3、T4、FT3、FT4 all show no obvious effect on postoperative function of thyroid.There is positive linear correlation between total thyroid weight,remnant weight,remnant ratio and postoperative function of thyroid. Conclusion:Total thyroid weight and remnant weight are an important factor affecting postoperative function of thyroid. We advocate that multiple regression equation should be used to determine both preoperatively and postoperatively the thyroid remnant weight of primary hyperthyroidism.