Objective: The paper analyzes the main influencing factors of inpatient costs of medical insurance patients in a tertiary hospital in Panzhihua City of Sichuan Province after the implementation of DRG payment to provide decision-making basis for hospitals to reasonably control the growth of inpatient costs and reduce the risk of possible loss and medical insurance departments to develop DRG payment standards. Methods: The objects of study were all the medical insurance inpatients who were included in DRG payment in the hospital in 2021, and the home page information of their medical records was collected, modeled by BP neural network, and compared with the results of multiple linear regression to analyze the influencing factors of medical insurance patients' hospitalization costs. Results: Both the BP neural network model and the multiple linear regression model fit the data well. The results of both models showed that hospitalization days, transfer, blood transfusion, and surgery were the main influencing factors on the hospitalization cost of patients under DRG payment. Conclusions: The application of BP neural network model in the study of factors affecting hospitalization expenses works well and has great practical significance. For the main influencing factors of hospitalization cost, hospitals should take measures to reasonably control the cost and reduce the risk of possible loss under DRG payment, meanwhile, the medical insurance departments should consider incorporating the influencing factors into DRG for the subdivision group to make the payment more scientific and reasonable.