In this paper, the dynamic behavior of internal structure of 1+1-dimensional ballistic deposition model is simulated by means of Kinetic Monte Carlo. The dynamic behaviors of the porosity and internal interface are investigated. It is found that the porosity, with the standard Gaussian distribution, increases very fast at the initial times and reaches a saturation valve, which is independent of the linear substrates. In addition to the surface width, the new method of extreme statistics is also employed to analyze the dynamic behavior of internal interface. The results show that the evolution of the internal interface of 1+1-dimensional ballistic deposition model satisfies the standard Family-Vicsek scaling, and belongs to the universality class described by the Kardar-Parisi-Zhang equation. Finally, the finite-size effects obtained by the two theoretical methods, i.e., surface width and extreme statistics are compared.