Abstract: Objective To compare the diagnostic performance of mediastinum window and specific window of pulmonary embolism(PE window)for the detection of acute pulmonary embolism with CT pulmonary angiography (CTPA) as the reference standard. Methods A total of 102 cases with central and interlobar pulmonary embolism diagnosed by CTPA were retrospectively analyzed. Additionally, 102 negative cases were recruited as the control group. The diagnostic confidence were recorded by two residents (R1 and R2) in routine soft tissue window (W=350 Hu, L=50 Hu) and PE window (W=120 Hu, L=65 Hu), respectively. The residents determined positive or negative PE respectively, only precisely located PE between the central or proximal lobes was considered to be true positive. Nonparametric tests of two paired samples were used to compare the diagnostic confidence index of PE using mediastinal window and "PE window". Results In 102 PE positive cases, 68.6% involved the central pulmonary artery, 31.4% involved the interlobular pulmonary artery alone, and 70.2% involved both sides. The true sensitivity and specificity of the two readers were 62.7% and 55.9%, 67.6% and 70.6%, respectively. Through the "PE window" of CT plain scan, the diagnostic confidence of PE was significantly improved (P = 0.016 and 0.014 respectively). Conclusions The use of CT plain scan "PE window" has a moderate diagnostic value for acute PE, but the use of "PE window" has a higher diagnostic confidence.