Although single-atomically dispersed metal-N_x on carbon support (M-NC) has great potential in heterogeneous catalysis, the scalable synthesis of such single-atom catalysts (SACs) with high-loading metal-N_x is greatly challenging since the loading and single-atomic dispersion have to be balanced at high temperature for forming metal-N_x. Herein, we develop a general cascade anchoring strategy for the mass production of a series of M-NC SACs with a metal loading up to 12.1 wt%. Systematic investigation reveals that the chelation of metal ions, physical isolation of chelate complex upon high loading, and the binding with N-species at elevated temperature are essential to achieving high-loading M-NC SACs. As a demonstration, high-loading Fe-NC SAC shows superior electrocatalytic performance for O₂ reduction and Ni-NC SAC exhibits high electrocatalytic activity for CO₂ reduction. The strategy paves a universal way to produce stable M-NC SAC with high-density metal-N_x sites for diverse high-performance applications.