Objective: Medication errors in hospital outpatient pharmacy have a serious negative impact on people’s health and economy. To assess the efficiency of 12-year refined management using PDCA cycle on reducing the dispensing errors in a large-scale hospital outpatient pharmacy. Methods: A retrospective study of dispensing errors was performed. Data for dispensing errors, stocks and accounts management from 2008 to 2019 was collected from the electronic system and evaluated using direct observation method. Results: The consistent rate of the stocks and accounts was significantly increased (86.93% vs 99.54%, p < 0.05). A remarkable reduction of error rate was achieved (0.014% vs 0.0006%, p < 0.05) and the rate of dispensing errors was significantly reduced (0.019% vs 0.000034%, p < 0.05). Besides, the technicians improved themselves during this procedure. Conclusion: the refined management using PDCA cycle was helpful to prevent the dispensing errors and improve medication safety for patients.