UV-resistant substances violacein have attracted much attention for the antioxidant properties such as inhabiting extreme environments. Herein, semi-empirical non-adiabatic dynamics simulations were employed to explore the S1 excited-state photochemical properties of violacein. After the system is excited to the Franck-Condon region, it relaxed to the S1 minimum. Subsequently, the single bond between 5-hydroxyindole and 2-pyrrolidone and the double bond between 2-pyrrolidone and oxindole were both twisted during deactivation to the conical intersection, and the 2-pyrrolidone ring was distorted with pyramidalization of a carbon atom. After passing through the conical intersection, the system returns to the ground state fastly. In non-adiabatic dynamics, it was found that 88.5 % of trajectories successfully returned to the ground state within 1 ps of the simulation time. In conclusion, we propose an excited-state deactivation mechanism for violacein system in vacuum, which will provide detailed mechanistic insights for similar light-shielding substances.