Background: Korea set up new diagnosis related group (DRG) as demonstration project in 2009. The new DRG was reformed in 2016. The main purpose of study is to identify the effect of reform on accuracy of payment. Methods: This study collected inpatient data from a hospital which contains medical information and cost from 2015 to 2016. The dependent variables were accuracy of total, bundled, unbundled payment, and payment for procedures. To analyze the effect of reform, this study conducted a multi-variate regression analysis adjusting for confounding variables. Results: The accuracy of payment increased after policy reform. The accuracy of total, bundled, unbundled payment, and payment for procedures significantly increased 3.90%, 2.92%, 9.03%, and 14.57% after policy reform, respectively. The accuracy of unbundled payment showed the largest increase among dependent variables. Conclusion: The results of study imply that policy reform enhanced the accuracy of payment. The government needs to monitor side effects such as increase of non-covered services. Also, leads to a considerable improvement in the value of cost unit accounting as a strategic play a role in development of DRG.