Abstract: Objective To assess the value of color doppler ultrasonography(CDUS) and emission-computed tomography in differential diagnosis benign thyroid nodules from malignant nodules with low echo level. Methods Retrospectively, two high qualification doctors respectively analysed the characteristics of forty-one thyroid nodules on imaging pictures with double blind methods, and then made the diagnosis. Compared with pathology, comparison of ROC curves of the two methods were drawn, and the diagnostic sensitivity,specificity,positive predictive value,negative predictive value and accuracy rate of color doppler CDUS and single photon emission-computed tomography(ECT) in differential diagnosis of benign and malignant were evaluated. Results Compared with pathology, of the forty-one nodules, twenty-seven thyroid nodules were benign and fourteen thyroid nodules were malignant. Twenty-four malignant thyroid nodules and seventeen benign thyroid nodules were diagnosed by CDUS.Thirty-nine malignant nodules and two benign thyroid nodules were diagnosed by ECT. The diagnostic sensitivity,specificity,positive predictive value,negative predictive value and accuracy rate of CDUS and ECT were 88.9%,100.0%,100.0%,82.4%,92.7% and 92.6%,14.3%,67.5%,50.0%,65.9%, respectively. The areas under the curves of US and ECT were 0.95 and 0.53, respectively. There was statistical difference between the two methods(P<0.0001). Conclusion CDUS has higher diagnosis value in differentiating malignant thyroid nodules from those that are benign than ECT.