Objective To understand the urine iodine level before 131I treatment in patients with differentiated thyroid cancer （DTC） and to analyze its influencing factors, in order to provide a reference for carrying out targeted dietary care intervention.Methods A convenience sampling method was used to select 215 patients with DTC who completed urine iodine testing prior to 131I treatment, then they were investigated by using a general information questionnaire, the Fear of Progression Questionnaire Short Form, and the Family APGAR Index.Results The urine iodine ＜200 μg/L before 131I treatment was found in 153 patients （71.2%） and ≥200 μg/L in 62 patients （28.8%）.Consumption of iodized salt, frequency of eating out, duration of low iodine diet, fear of disease progression, and family function were the influencing factors of urine iodine level before 131I treatment in patients with DTC （all P＜0.05）.Conclusion The urine iodine level for most DTC patients prior to 131I treatment is within the range of recommended therapy, while there are still some patients who have poor low iodine preparation prior to 131I therapy.Medical staff should strengthen dietary guidance to patients, stress the control of iodized salt intake, decrease the frequency of eating out, and enhance the care from family members, in order to effectively control patients′ urine iodine level before 131I treatment, improve the treatment outcome, and promote patients′ recovery.