Objective To explore the value of chest CT value in the differential diagnosis of pleural effusion. Methods A total of 81 patients with pleural effusion were included in this study, including exudate, transudate, malignant pleural effusion and benign pleural effusion.The ROC curve of average CT value was established and the area under the curve was calculated. Results Among 81 patients with pleural effusion, 59 cases were exudative, 22 cases were transudative, 33 cases were malignant pleural effusion and 48 cases were benign pleural effusion.The mean CT value of the exudate group, (16.68±6.76) Hu, was significantly higher than (5.50±3.42) Hu of the transudate group (P<0.000 1).ROC curve analysis showed that the mean CT value of pleural effusion had high accuracy in distinguishing exudate from transudate (area under the curve was 0.9445).When the cut-off value for exudative effusion was over 9.99 Hu, the sensitivity and specificity were 88.14% and 90.91%, respectively.The mean CT value of malignant pleural effusion group, (15.38±7.29) Hu, was not significantly different from (12.45±8.03) Hu of benign pleural effusion group (P=0.098 1). Conclusions In the differential diagnosis of pleural effusion, the chest CT value can be used to identify transudate and exudate, but not benign and malignant pleural effusion.