Situation assessment in interactions needs to make an explicit evaluation of the social interactions. When there is more than one agent or “player”, the logic of knowledge and belief play an important role. One is interested not only in each person’s knowledge and beliefs about substantive matters, but also in his knowledge and beliefs about the others. This paper explored the meta-synthetic computing formula of situation assessment in social interactions. First, each person’s knowledge and belief determines the interactive structure, which can be computer-aided calculation. Second, the process of interactions is dynamic, the assessment needs an open interactive environment to analyze and understand the situation, which is human-computer symbiotic. Third, these interactions are supported by the data and information processing algorithm and models. Interactive structure aided by computer, human-computer symbiotic open interactive environment, data and information processing algorithm and models constitute meta-synthetic computing formula of situation assessment.