Objective To explore the structure and influencing factors of overall medical treatment expenses of 1 635 inpatients of Wenchuan earthquake in West China Hospital and to provide references for setting up the criteria of medical expenses and for assess the cost-effect of medical rescue and treatment. Methods The data of earthquake casualties were collected to analyze the constitution and influencing factors of the overall medical expense by SPSS 13.0 software. The data were described by X±SD. Comparison of data categories was tested by rank sum and influencing factors were analyzed by multi ple l inear regression analysis. Results A total of 1 635 casualties including 1 413 (86.04%) earthquake wounded and 222 (13.96%) patients from the disaster area were identified. The average expense per capita was 9 165.05±12 426.11 yuan. The overall cost was made up of operation expenses (71.75%) including material cost, examination fee and treatment fee, drug cost (18.41%) as well as bed fee and others (less than 10%). The cost of patients from the disaster area was higher than that of the earthquake wounded (Z= –4.109, P=0.000). The operation, compl ications, multiple-site damages, injures induced by the secondary disaster of the earthquake such as burn and corrosion were the direct reason leading to the high overall expense. The influencing factors included operation (r=0.386), ICU (r=0.336) and the day of hospital ization (r=0.246). Conclusion The earthquake wounded occupy the predominant percentage of the earthquake inpatients in West China Hospital. The operation, compl ications, multiple-site damages and injures induced by the secondary disaster of the earthquake lead to a high overall expense. The influencing factors include operation, ICU and the day of hospital ization. The relationship between the expense and the disease category largely depends on the classification criteria. The relationship between the expense and the age as well as the prognosis needs further study. But no correlation between the expense and the gender is found.