Semiconductors are the foundation of the information revolution. However, our current understanding of some basic properties of semiconductors is still very limited. Here, I will introduce some of our computational research progress on complex defect structures and nonlinear optoelectronic properties in semiconductors. In the first part, I will introduce the formation mechanism of complex structural reconstruction on the silicon surface, one-dimensional line defects in GaN, and a new mechanism for epitaxial growth of nitride films, the dynamic evolution of defects in semiconductors under extreme non-equilibrium conditions. In the second part, I will introduce how to control the bulk photovoltaic effect in semiconductors through external fields.