Objective To explore the thromboembolic events and mortality in patients with different types of severe pneumonia, and to analyze the related high-risk factors. Methods A total of 161 severe pneumonia patients who admitted in intensive care unit from January 2018 to February 2023 were included in the study. The patients were divided into a COVID-19 group (n=88) and a community-acquired pneumonia (CAP) group (n=73) according to the type of pneumonia, and divided into a thrombosis group and a non-thrombosis group according to the occurrence of thrombosis. The patients were followed-up until discharge or in-hospital death, registering the occurrence of thrombotic events. Results During the in-hospital stay, 32.9% of CAP and 36.4% of COVID-19 patients experienced thrombotic events (P>0.05). In CAP group all the events (including 24 paitents) were venous thromboses, while in COVID-19 group 31 patients were venous and 3 were arterial thromboses (2 were cerebral infarction, and 1 with myocardial infarction). There were statistically significant difference in gender, age, venous thromboembolism score (VTE score), activated partial thromboplastin time (APTT), and procalcitonin (PCT) between the TE group and the Non-TE group. Logistic regression analysis showed that thrombotic events was associated with sex, age and APTT; gender (female: OR=2.47, 95%CI 1.13 - 5.39, P<0.05) and age (OR=1.04, 95%CI 1.01 - 1.07, P<0.05) were positively associated with thrombotic events. During the in-hospital follow-up, 44.3% of CAP patients and 42.5% of COVID-19 patients died (P>0.05). Receiver operator characteristic (ROC) curve analysis showed that APACHEⅡ score was more accurate in predicting mortality of severe pneumonia, and the area under the ROC curve (AUC) was 0.77 (95%CI 0.70 - 0.84, sensitivity 74.3%, specificity 68.1%), the AUC of the VTE score was 0.61 (95%CI 0.53 - 0.70, Sensitivity 31.4%, specificity 81.7%); the AUC of the creatinine was 0.64 (95%CI 0.56 - 0.73, sensitivity 72.9%, specificity 51.2%). While the Kappa value for kidney disease was 0.409 (P<0.05) presenting moderate consistency. Conclusions The incidence of thromboembolic events and mortality are high in patients with different types of severe pneumonia. Thrombophilia was associated with sex, age, and APTT. APACHEⅡ score, VTE score, and creatinine value were independent risk factors for predicting death from severe pneumonia.