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】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（1 point = uninterpretable, 2 point = moderate confidence in diagnose, 3 point = high confidence in diagnose）were record by two residents (R1 and R2) in routine soft tissue window (W=350, L=50) and PE window (W=120, L=65), respectively. Two matching samples of non-parametric test was used for data analysis. The residents determined positive or negative PE respectively, only PE with precisely location was considered to be true positive one. 【Results】68.6% of the PE involved central pulmonary, 31.4% involved interlobar pulmonary and 70.2% involved the bilateral pulmonary artery. The sensitivity of PE window by two readers were 62.7% and 55.9%，the specificity were 67.6% and 70.6%. Confidence in the diagnosis of PE was significantly improved by PE window in unenhanced CT (P values were 0.016 and 0.014, respectively). 【Conclusions】PE window in unenhanced CT has moderate diagnostic value for acute PE, the use of PE window has higher diagnostic confidence for readers