Objective: To analyze the clinical characteristics of patients with rheumatoid arthritis (RA) complicated with venous thrombosis of lower extremities, and to improve the awareness of this condition. Methods: The clinical and laboratory data of 502 RA patients hospitalized in Department of Rheumatology and Immunology Peking University Third Hospital from November 1, 2013 to December 31, 2020 were collected, retrospective analysis was made on the RA patients who were diagnosed with lower limb vein thrombosis on discharge but hadn't on admission, the patients in this group were defined as thrombosis group, and the other patients without lower limb vein thrombosis were taken as control group. Single factor analysis was conducted between the two groups. Then multivariate Logistic regression analysis was used to analyze the independent risk factors of RA complicated with lower limb venous thrombosis with statistical significance in univariate analysis. Results: There were 34 patients (6.77%) in the thrombosis group and 468 patients (93.23%) in the control group. The age of thrombosis group was 34-86 years (median age was 71 years); 23 were female and 11 were male; there were 20 cases with unilateral lower limb vein thrombosis and 14 cases with bilateral lower limb vein thrombosis; pulmonary embolism in 3 cases (low risk).In the thrombosis group 17 (50.0%) patients were bedridden for more than one week or needed crutches/wheelchairs before admission. 29 cases(85.3%)had large joint involvement of lower extremities, including 22 cases of knee joint involvement, 1 case of hip joint involvement, 2 cases of ankle joint involvement, and 4 cases with both knee and hip joint involvement. In the thrombosis group, the high, middle and low disease activity scores 28(DAS28) were 23 (67.6%), 9 (26.5%) and 2 (5.9%), respectively. There were 21 patients in the thrombosis group had completed thrombosis related examinations, only 4 patients were positive for anti-cardiolipin antibody or anti-β2 glycoprotein 1 antibody or lupus anticoagulant, the rests were all negative. In the thrombosis group, age and platelet (PLT) level were significantly higher than those in the control group [71 (60, 77) years vs. 60 (51, 68) years, Z=-3.873, P < 0.01, (328.53× 10⁹±119.06 × 10⁹) /L vs.(278.68 × 10⁹±104.50 × 10⁹)/L, t=2.660, P < 0.01, respectively]. The proportion of D-Dimer increased in the thrombosis group as well as the positivity rheumatoid factor (RF) was much higher than those in the control group (94.1% vs.66.4%, χ²=11.192, P < 0.01; 85.3% vs.67.1%, χ²=4.852, P < 0.05, respectively). Multivariate Logistic regression analysis showed that age (OR=1.063, 95%CI: 1.026-1.101, P=0.001), D-Dimer increased (OR=4.968, 95%CI: 1.136-21.730, P=0.033) and PLT level (OR=1.004, 95%CI: 1.001-1.007, P=0.022) were the independent risk factors for RA complica-ted with lower extremity venous thrombosis. Conclusion: RA patients have potential risk of thrombosis of lower extremities. For the older age, D-Dimer and PLT elevated, especially those who were bedridden, RF positive and had high disease activity, should be alert to the risk.