The ratio of radiation energy density to matter energy density is an important parameter to distinguish the characteristic of atomic processes in plasma. Actoring to this parameter, atomic processes in plasma can be divided into two typical categories: collision-dominated and radiation-dominated. According to numerical simulation, atomic processes of these two categories have different characteristics. The LTE state can be quickly reached in the collision-dominated plasma. However in the radiation-dominated plasma, the temperature of bound electrons, the ionization degree, and the temperature of free electrons have different relaxation time scales. There is some kind of quasi-LTE state.