Objective: To analyze the impact of integrating urban resident basic medical insurance and the Rural New Cooperative Medical Scheme (referred to as urban and rural resident basic medical insurance after integration) on inpatient expenses in Beijing, and to quantitatively estimate the proportion of unreasonable increase of inpatient expenses. Methods: Secondary and tertiary hospitals’ discharge records in Beijing from 2017 to 2018 and Beijing Health Services Survey in 2018 (BHSS 2018) were used, with a difference in difference model and a log-linear model. Results: The integration of residents’ medical insurance schemes increased the reim- bursement for urban and rural resident basic medical insurance (URRBMI) inpatients and their accessibility to inpatient services, which was also accompanied by an increase in hospitalization costs. The insurance integration resulted in an increase of average annu- al hospitalization cost by about 587 yuan per inpatient, of which the unreasonable increase accounted for 32.0%. After the reform, ex- penditure of medical insurance fund increased by about 1 237 yuan per inpatient, of which 9.1% was unreasonable increase. Conclu- sion: The payment system of medical insurance and the budget management capacity of basic medical insurance fund should be fur- ther improved, and the mechanism for monitoring and adjusting medical insurance policies should be optimized.