The invention belongs to the technical field of biology and particularly relates to a cellular agent and a preparation method and application thereof. The cellular agent comprises Treg cells, IL-4, salvia extracts and medically acceptable solvents, wherein the Treg cells are 5X10<6>-1X10<7>/mL in concentration; the IL-4 is 5-20ng/mL in concentration; the salvia extracts are 1-5mg/mL in concentration. The invention further provides the preparation method of the cellular agent and the application of the cellular agent in preparing drugs used for preventing and treating skin eczema. The cellular and the preparation method and application thereof have the advantages that the Treg cells are high in safety and effectiveness and can play a role synergically with the IL-4 and the salvia extracts; in addition, the Treg cells obtained via expansion in vitro are good in state, fast in growth and low in manufacturing cost.