Objective To compare different delayed scanning methods in multi-slice spiral CT angiography (MSCTA)in diagnosis of pulmonary embolism (PE). Methods Sixty patients with suspected PE were divided into three groups (A, B and C). MSCT with same Iodine concentration, injection rate, contrast medium but different delayed scanning methods was performed after injection of contrast medium. Patients in group A were examined with fixed time method (15 s), in group B with small dose-density curve method, while in group C with contrast medium track and triggering technoligy. The number, position and the shapes of emboli were evaluated with MIP, MPR and VR. Results The successful examination rate of group A was 55.00% (11/20), while of group B and C was both 100%. The coincidence rate of MSCTA compared with DSA in each group was 96.04% (291/303). Conclusion The best delayed scanning method in MSCTA for diagnosis of pulmonary embolism is contrast medium tracking and triggering technology.