Objective To analyze outpatient pharmacy internal prescription dispensing errors list and raise suggestions on preventive measures, in order to provide better and safer medical service for patients. Methods We summarized and analyzed the prescription dispensing error types and causes based on 320 cases of internal prescription dispensing errors of the outpatient pharmacy in a hospital of the highest rank between January and June 2014. Then, we put forward suggestions on improvement measures. Six months after the implementation of these measures, we compared the error rate after dispensing between January and June 2014 with those between July and December 2014. Results Among all the 320 prescription dispensing errors, 120 (37.50%) were wrong medication amount, 101 (31.57%) were wrong drugs, 76 (23.75%) were wrong usage and dosage, 17 (5.31%) were wrong packaging specification, and 6 (1.87%) were wrong medication form. The dispensing error rate between July and December 2014 was reduced compared with the rate between January and June 2014. The error rate after dispensing declined from 0.01‰ to 0.006‰. Conclusion Encouraging drug dispensing personnel to issue internal dispensing error recording list for the staff who had errors in dispensing, promoting pharmacists’ professional quality, strengthening the management of outpatient pharmacy, reasonable storage of medicines, enhancing intervention of irrational prescriptions, improving the spatial layout of the pharmacy, and perfecting dispensing error management system, can in a large extent reduce medication errors.