Abstract: The participation of Hong Kong and Macao in the practice of China's state governance is an organic component of the modernization of China's system and capacity for governance in contemporary China. From the perspective of great history, Hong Kong and Macao's participation in the practice of state governance is accompanied by the history of New China and the history of reform and opening-up. Nevertheless, it has not attracted enough attention from the academic circles so far. From the perspective of public participation, it is of great significance to explore the three basic issues of "who participate", "what to participate" and "how to participate" for clarifying the theoretical connotation of Hong Kong and Macao's participation in China's state governance. "Who participate" includes Hong Kong and Macao's individuals, social organizations, administrative organs and other participants; "What to participate" covers the public affairs from global, national, cross-tariff border to local level; "How to participate" is embodied in the specific ways for Hong Kong and Macao to participate in political life, economic construction, social livelihood and public administration. The inherent characteristics of Hong Kong and Macao's participation in the practice of state governance reflect the gradual expansion from the conscious participation of individual actors to the legal participation of organizational actors, the gradual shaping of the multi-level affairs system of China's state governance from "outside" to "inside", and the gradual evolution track from single participation to inclusive participation. Under the policy of supporting better integration of Hong Kong and Macao into the development of the country, the connotation and patterns of Hong Kong and Macao's participation in China's state governance practice deserve continuous observation and research.