Diagnostic criteria for acute pulmonary embolism, including the following: 1. Clinical manifestations: cough, chest pain, hemoptysis, dyspnea, etc.; 2. Physical examination: heart murmur caused by tricuspid valve closure insufficiency, and right heart enlargement on percussion. Body circulation stasis manifests as lower limb swelling, and unilateral lower limb swelling when there is deep vein thrombosis in the lower limbs; 3, laboratory: positive D-dimer test, increased troponin, decreased oxygen saturation, decreased carbon dioxide, and significantly increased alveolar-arterial oxygen partial pressure difference; 4, imaging: pulmonary artery CT angiography shows pulmonary artery filling defect, cardiac ultrasound shows increased right heart load, and lower limb vascular ultrasound suggests Deep vein thrombosis in the lower extremities; other tests include pulmonary ventilation and perfusion scan, magnetic resonance angiography, etc. Ultrasound of both lower extremities is helpful to investigate the source of thrombosis.