Objective To summarize the clinical manifestation and the causes of lower limb deep venous thrombosis （DVT） complicated with pulmonary embolism （PE）. Method The clinical data of 45 cases of PE confirmed by CTPA from May 2009 to May 2012 in this hospital were summarized retrospectively. Results Five patients with PE had no obvious clinical manifestation， 9 patients （20.0%） had chest stuffiness and short of breath， 8 patients （17.8%） had cough. In the causes of thrombosis defluxion：11 patients （24.4%） had early mobilization after operation， 9 patients （20.0%） had functional exercise after operation， 7 patients （15.6%） had turn over or defecate on bed， 2 patients （4.4%） had sneeze， 14 patients （31.1%） had no definite causes. Conclusions Patients with lower limb DVT have high risk of thrombosis defluxion， although adequate anticoagulation. Early mobilization， functional exercise， and transient increased abdominal pressure are easy to lead to thrombosis defluxion， so lead to PE. Absence of the protection of inferior vena cava filter， patient should be required for bed ridden in order to avoid the thrombosis defluxion.