Objective To determine the correlation of plasma level of D-dimer (DD) with clot burden of pulmonary embolism. Methods A prospective study was performed on 69 consecutive patients with acute pulmonary thromboembolism (PTE) confirmed by computed tomographic pulmonary angiography (CTPA) in our hospital from January 2009 to August 2011. A pulmonary artery obstruction index (PAOI, Mastora score) ＞21.3% indicated severe obstruction of PTE. A right ventricle/left ventricle (RV/LV) ＞0.9 indicated RV dysfunction. The plasma level of DD was determined by immunoturbidimetric assay. Results The median DD level was 765μg/L (95%CI: 750?1 205μg/L) and that of PAOI was 16.77% (95%CI: 16.32%?23.06%). Plasma DD level was positively correlated with PAOI (r＝0.417, P＝0.000). The patients with PAOI ＞21.3% had significantly higher DD levels than those with PAOI ≤21.3% (993 vs 663μg/L, Z＝-2.991, P＝0.003). DD level was positively correlated with RV/LV (r＝0.272, P＝0.024). The patients with RV/LV ＞0.9 had obviously higher DD levels than those with RV/LV ≤0.9 (880 vs 634μg/L, Z＝-2.070, P＝0.038). There was a positive correlation between PAOI and RV/LV (r＝0.390, P＝0.001). Negative correlation was found in the PTE onset time with DD level (r＝-0.407, P＝0.000), but not with PAOI (r＝-0.140, P＝0.245). There was no significant difference in the DD level and PAOI between the elderly patients (＞60 years old) and those younger (≤60 years old) (727.0 vs 792.5μg/L, Z＝-0.180, P＝0.857; 14.84% vs 20.97%, Z＝-1.382, P＝0.167). After 3 months’ standard anticoagulant therapy, both DD level and PAOI were decreased in the cohort (Z＝-6.976, P＝0.000; Z＝-7.009, P＝0.000), and their decreases were correlated (r＝0.609, P＝0.000). Conclusion DD level is positively correlated with CTPA clot burden and RV/LV respectively, and is helpful in illness assessment, management guidance and prognostic evaluation for the acute PTE patients. There is no significant difference in DD level and PAOI between the patients older and less than 60 years.