Objective To explore the quantitative influence factors of early hypothyroidism(EH) in ¹³¹I treatment of patients with graves disease (GD). Methods The thyroid mass, iodine uptake rates, age, gender, illness course and anti-thyroid drugs (ATD) in GDs patients with ¹³¹I treatment were recorded and used for the analysis of influence factor of early hypothyroidism. Results In all ¹³¹I treated GDs patients, there were no statistically significant difference on cure rates and incidence of EH (P＞ 0.05), no matter male or female, the first ¹³¹I treatment or second treatment. The EH rate of the ¹³¹I treated GDs patients with their thyroid mass less 30g was significantly higher than that of >31g(P＜0.05 ). There was no significant difference on EH rates for patients with 24h thyroid iodine uptake between 45%～95%(P＞0.05), the patients between the age of 21to 65 years(P＞0.05). The relationship between the EH rate and the age appeared to be ∪ type trend, and the thyroid was more susceptible to radiation damage over the age of 20 (P＜0.05). The EH rate of the patients with GD duration more than 6 months, and between 510 years showed increasing tendency with the extension of the course, but the difference between them was not statistically significant(P＞0.05). The EH rate for patients before and after ATD treatment had a significant difference ( P＜0.01). Conclusion The thyroid mass, age and ATD may be the main influence factors to induce the early hypothyroidism in the ¹³¹I treatment patients with GD.