Objective To analyze the effect of diagnosis related groups (DRG) payment method reform on hospital disease group structure. Methods Taking the only one class Ⅲ level A hospital from a city as a sample hospital, the settlement data of hospitalized cases enrolled according to China Healthcare Security Diagnosis Related Groups (CHS⁃DRG) 1.0 grouping protocol were extracted from 2017 to 2019, and 2021. The basic conditions of hospitalized cases in the hospital during 4 years were analyzed. The service mix Herfindahl⁃Hirschman index (SPEC) was used to describe disease group structure concentration of the hospital. The interrupted time series analysis (ITSA) was employed to evaluate variation tendency of SPEC in the hospital before and after DRG payment method reform. The multiple linear regression model was used to analyze the influencing factors for disease group selection preference in the hospital. Results (1) From 2017 to 2021 (excluding 2020), the overall weight, number of DRG disease groups, and case mix index presented as an increased tendency. (2) The results of ITSA revealed that before reform, SPEC of the hospital decreased by 0.0002 per month (P<0.05), but after reform, SPEC increased by 0.0005 more per month than before reform (P<0.05), namely, after reform, SPEC increased by 0.0003 per month. (3) After reform, when the weight of DRG disease groups increased by 1, the growth rate of DRG disease groups' proportion increased by 6.114% as compared with before reform (P<0.05); in addition, when the market share of DRG disease groups increased by 1%, the growth rate of DRG disease groups' proportion increased by 1.066% as compared with before reform (P<0.05). Conclusion The DRG payment method reform makes the sample hospital shrinks the scope of inpatient services, and the structure of disease groups is more concentrated; moreover, the sample hospital pays more attention to the development of difficult disease groups in line with their own functional positioning after reform.

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