The situation is considered that the information diffusion is limited by the full coverage goal in online social networks. The existence of full coverage agent group of information diffusion is
discussed together with the finding algorithm under the community information sharing mode. First, the channel network model of information diffusion is constructed using network model and information diffusion mechanism of community information spread. Second, it is proved that the minimum dominating set is a satisfactory solution to the full coverage problem of information diffusion by means of mathematical reasoning. Finally, a heuristic search method is used to design an algorithm to find the full coverage agent group of information diffusion and the effectiveness of the algorithm is also analysed. Compared with the traditional two step information diffusion mechanism, the effect of the agent group sharing model proposed in this paper is more stable and predictable.