D-dimer testing is performed in AF Patients receiving warfarin therapy (target INR:1.5-2.5) in Wuhan Asia Heart Hospital. Patients with elevated d-dimer levels (>0.5ug/ml FEU) were SCREENED AND RANDOMIZED to three groups at a ratio of 1:1:1. First, NOAC group,the anticoagulant was switched to Dabigatran (110mg,bid) when elevated d-dimer level was detected during warfarin therapy.Second,Higher-INR group, INR was adjusted to higher level (INR:2.0-3.0) when elevated d-dimer level was detected during warfarin therapy. Third, control group, patients with elevated d-dimer levels have no change in warfarin therapy. Warfarin is monitored once a month by INR ,and dabigatran dose not need monitor. All patients were followed up for 24 months until the occurrence of endpoints, including bleeding events, thrombotic events and all-cause deaths.