Abstract: Objective To study the distribution of blood clots in lungs in patients with lower extremity deep vein thrombosis combined acute pulmonary embolism, and explore the clinical effect of small dose urokinase thrombolysis. Methods A total of 80 cases of lower extremity deep vein thrombosis combined acute pulmonary embolism in our hospital between January, 2014 and January, 2016 were enrolled and randomly divided into observation group (40 cases) and control group (40 cases). The control group received anticoagulation with warfarin following by heparin therapy, while the observation group received additional small dose of urokinase thrombolysis treatment. The blood clots distribution in lung, laboratory test results and effective index for lower limb thrombus were compared before and after the treatment. The relief of clinical symptoms was observed at d₅ and d₁₄. Results Thrombosis in 3 branches of pulmonary artery was common, following by 2 branches of pulmonary artery, there was no significant difference between the two groups (P > 0. 05). After 5 days treatment, the remission rate of chest pain and dyspnea in the observation group was significantly higher than that in the control group, the difference was statistical significant (P < 0. 05). Two weeks after the treatment, the remission rate of chest pain and dyspnea in the observation group was similar with the control group, the difference was not statistical significant (P >0. 05); the remission rate of cough response in the observation group was significantly higher than that in the control group, the difference was statistical significant (P < 0. 05). There was significant difference in the level of D-Dimer (P <0. 05), but not in the levels of PLT, INR and NT-pro BNP (P > 0. 05), between the two groups. The effective rate for lower extremities thrombosis treatment was 34. 98% in the control group and 67. 87% in the observation group, the difference between the two groups was statistical significant (P < 0. 05). Conclusion Thrombosis can occur in 3 (most common) or 2 branches of pulmonary artery in patients with lower extremity deep vein thrombosis combined acute pulmonary embolism. The small dose of urokinase thrombolysis combined with anticoagulant therapy can effectively relieve chest pain and dyspnea in a short time as compared with anticoagulant therapy along, thrombolysis is obviously without increasing the long-term risk of bleeding. It is a highly efficient and reliable therapeutic method.