Objective: The paper analyzes the structure of DRG groups with the degree of structural variation to provide a data analysis method for finding out the hospital's illegal adjustment of DRG groups. Methods: Using the evaluation indicators of values of structure variation|degree of structure variation and contribution rate of structure variation|the DRG groups and the number of violation cases of 345 hospitals in Hangzhou in 2020 and 2021 were analyzed. Results: With the increase of contribution rate of structure variation in the interval|the proportion of illegal cases in the total number of inpatient cases in the interval showed an increasing trend. The increase of contribution rate of structure variation in the disease group could reflect the growth trend of violations in medical institutions to a certain extent and there was a positive correlation between them. Conclusion: The analysis of DRG groups structure with the degree of structure change can reflect violations of hospitals|which can be applied in strengthening the medical records supervision in the DRG payment reform.