Based on the theory of human-system interaction theory, this paper adopts MEC theory to design the interview content, and extracts the influence factors and the relationships among them. The structure model is explained by the explanation structure model from the three levels of system layer, human-system interaction layer and user layer. The analysis results show that the older users to boycott the root cause of the mobile social media is a mobile social media did not meet older users use expectations, tend to use familiar social style and user's information literacy is weak. This study can help social media developers more in-depth understanding of information behavior characteristics of elderly vulnerable groups, for the government to strengthen the protection of the rights and interests of the elderly of network information, offer reference for mobile social media developers provide guidance for the elderly to provide a more reasonable information service.