Abstract: In order to predict the damage initiation and destruction process of composite box accurately, the progressive damage finite element analysis technique of integral multi-spar composite box which took material failure into consideration was investigated. Based on ABAQUS software, the progressive damage analysis model of box was established firstly by using the material mechanical property parameters obtained by standard tests, and three dimensional Hashin failure criteria and square stress failure criteria were adopted as the failure criteria of composite ply and adhesive interface, respectively. Then, the solution for post-buckling loading capability of the integral multi-spar composite box was accomplished by the model, and the analysis model was validated by failure test. The results show that the finite element analysis results for loading capability and stress of structure coincide well with test values, and the failure mode predicted is also consistent with the test results. The errors of buckling load and loading capability are within 5%. The conclusions obtained show that the analysis model which takes failure of ply and debonding of interface into consideration can simulate the damage process of integral multi-spar box effectively.