This comparative case study aims to identify common factors that contribute to the differences in the protest waves of social movements in general by using a mechanistic approach to assess the political opportunities, mobilizing structures, and framing processes of the Umbrella Movement and the Anti-Extradition Bill Movement. These two protest waves are different in the emergences, longevities, and declines. An analytical framework is developed on the relationship between the independent variables and the dependent variables through mechanisms. The mechanisms are used as the intermediate variables between the IVs and the DVs, and the quantitative analysis on the IVs makes the mechanisms operational. This thesis adopts mixed methods. A quantitative approach of network analysis and protest event analysis fully examines the relationships between the IVs – actors (leaders, SMOs/groups, influential allies) & frames and DV – waves of protest which studied by protest event analysis. The qualitative approach of mechanisms is used to describe the impacts of the mechanisms – attribution of opportunity and threat, repression, radicalization, competition and diffusion. Specifically, the mechanistic approach is the overall methodological approach, and network analysis (social network analysis and discourse network analysis) and protest event analysis are specific methods. The original contribution to knowledge of this research was adopting a mechanistic approach based on a broader political process theory to the protest waves in hybrid regimes. Merely having the classic social movement theories – political opportunities, mobilizing structures and framing processes accessible is not enough for the explanation of the differences in protest waves. This thesis adds new knowledge to the theories field of Hong Kong’s democratic movements. It also has policy implication for the future of Hong Kong and the relationship between China and Hong Kong.