Objective To investigate the morphology,size and density characteristics of adult normal thyroid and to establish the normal reference range of thyroid.Methods 317 patients without thyroid disease underwent head and neck computed tomography angiography (CTA)examination from Jun.2011 to Jun.2012 in the First Affiliated Hospital of Chongqing Medical University.Their data were analyzed.The thyroid morphology including the outside angle,width,thickness,isthmus was observed and measured.Plain scan and arterial phase CT values of thyroid gland were measured.The age and sex of patients were recorded.The left and right lobe on the thyroid dimension and density were investigated,and the index 95％ normal reference range was calculated.Results ① Morphology:normal thyroid glands were butterfly-shaped on the axis,accounting for 95.9％(304/317),and absence of thyroid gland isthmus accounted for 4.1％(13/317).② There was no significant difference for the thyroid lateral angle between the lobes and sexes(P＞0.05).There was significant difference between age groups(P=0.00).The 95％ reference range:the outside angle was 111.7°± 31.6° in patients younger than 60 years old,and 101.3°± 36.7° in patients of or older than 60 years old.③ The dimensions of the right lobe were longer than those of the left.The dimensions of the lobes in males were longer than those in females.There was no statistical difference among decades(P＞ 0.05).There was no significant difference in the thickness of thyroid isthmus between genders and among different age groups (P＞ 0.05).95％ reference range of the thickness of thyroid isthmus was 1.1-7.3 mm.④ There was statistical difference for the plain scan and enhanced CT values between lobes and sexes and among age groups (P＜0.05).95％ reference range needed to be separately formulated between the lobes,sex and age＜30 years and ≥30 years.Conclusion Studying the morphology,size and density characteristics of adult normal thyroids can help to establish normal thyroid imaging anatomical data in this region,and provide reference basis for imaging diagnosis of thyroid disease.