The purpose of this paper is formalizing an informal group system model consists of the interpersonal relation system components that are emotinal balancing cellular automata designed by agent-based approach. The framework of the interpersonal relation system model is based on the general system theory and the social psychological interaction theories, that are Heider’s balance theory and Festinger’s cognitive dissonance theory. The individual system which composes of an informal group system model has the einvironment models. The environment models represent the pressure of emotion and any other things of the ncighbourhood.