How does the establishment of the National Supervisory Commission affect China’s capacity to curb corruption? Using published materials and fieldwork data, this article addresses this question by comparing the newly established single anti-corruption agency with the previous dual-track anti-corruption system. It firstly examines the previous system by focusing on four dimensions of the interaction between the Commission for Discipline Inspection (CDI) and the People’s Procuratorate (4Cs): complementarity, convergence, competition and conflict. Although the CDI and the procuratorate compensated for each other’s deficiencies, competition and conflicts between two institutions were rife, reducing the efficiency of China’s anti-corruption work. The article then investigates the double-edged effect of building the National Supervisory Commission.