With the rapid development of China’s Internet platform enterprises, the resulting problem of lack of social responsibility and governance of platform enterprises has become a social focus issue, and the key to solving this problem lies in fundamentally clarifying the structural dimensions and boundaries of social responsibility of Internet platform enterprises. Based on the social responsibility reports released by 12 local Internet platform enterprises, such as Alibaba, DDT and Meituan, this paper uses Nvivo 12.0 software to conduct open coding, spindle coding and selective coding on the original data, and takes advantage of the rooting theory analysis method to inductively extract the social responsibility of China’s internet platform enterprises. The results show that China’s internet platform enterprises’ social responsibility contains nine structural dimensions, namely, economic responsibility, political responsibility, legal responsibility, environmental responsibility, employee responsibility, user responsibility, partner responsibility, charity and public welfare responsibility, and industry ecological responsibility. Based on these dimensions, a pyramid model of internet platform enterprises’ social responsibility is constructed from the perspective of responsibility to stakeholders. The model contains three main levels, that is, bottom-line social responsibility, safeguarding social responsibility, and expectation social responsibility. This provides a new theoretical basis for further research and definition of the structural dimensions and system of social responsibility of internet platform enterprises. It also provides a theoretical reference for internet platform enterprises to improve their social responsibility system in practice.