Background: Device-related thrombosis (DRT) after successful closure implantation on left atrial appendage (LAA) was considered as a major challenge and optimal strategy on antithrombotic therapy remains to be solved. This study was performed to compare the clinical effectiveness and safety of reduced rivaroxaban dose (RRD) and dual antiplatelet therapy (DAPT) after left atrial appendage closure (LAAC) implantation with the Watchman device. Methods: After successful LAAC, consecutive participants were medicated with a standard DAPT or RRD. The primary endpoints included DRT, thrombosis events (TE), and bleeding events that were documented during a 12-month follow-up period. Results: 767 patients (DAPT: n = 140; RRD: n = 627) were initially included. After propensity score matching (PSM), 140 patients treated with DAPT and 280 patients with RRD were included in each group with similar baseline information, thromboembolic and bleeding risk factors, cardiovascular risk factors and concomitant medication. In the RRD group, 193 patients were on rivaroxaban 15 mg (R{}^{15}) and 47 received rivaroxaban 10 mg (R{}^{10}). The incidence of DRT was documented in 12 (9.3%) patients in the DAPT group and 3 (6.3%) in R{}^{10} and 7 (3.0%) in R{}^{15} (log-rank p = 0.050). DAPT subgroups were more likely to experience shorter time to DRT as compared to R{}^{15} (R{}^{15}vs. DAPT hazard ratio (HR) = 0.334, p = 0.015, 95% CI: 0.131–0.850). The median length of DRT in the R{}^{15} group was significantly lower than that of the DAPT group (1.721 [1.610–1.818] mm vs. 1.820 [1.725–1.925] mm, p = 0.029). Compared with the unadjusted estimated rates of ischemic events for patients with similar congestive heart failure, hypertension, age \ge75 years, diabetes mellitus, prior stroke or transient ischemic attack or thromboembolism, vascular disease, age 65–74 years, sex category (CHA{}_2DS{}_2-VAS{}_{\text{c}}) scores, a significant decrease of 68.6% in ischemic stroke rates was noted in the R{}^{15} group, which contributed to a 54.9% reduction of overall thromboembolic events. The overall minor bleeding was not significantly different amongst the three groups (p = 0.944). Procedural bleeding was more common in the DAPT group, as compared with the R{}^{10} and R{}^{15} groups. Conclusions: After successful closure implantation, long-term RRD significantly reduced the DRT and TE occurrence compared with DAPT.