Abstract: The interaction between low-energy protons (10 ~ 150 keV) and S781 white paint is simulated by using SRIM-2003 software. The stopping power of nucleus and electron, the energy loss related with ionization and displacements, and the range of the protons in S781white paint and in its two components of ZnO pigment and the binder are included in the simulations. The results indicate that the stopping power of electron is far greater than that of nucleus, and the radaition damage in S781 white paint is mainly due to ionization. Furthermore, our simulations also show that the ionization-related energy loss is mostly caused by ZnO pigment.