Precipitation strengthening is one of the most effective methods for achieving ultra-high strength. The properties and performances of steels are highly dependent on the characteristics of nanoscale precipitates. To further enhance the strength of steels, co-precipitation of two or multiple secondary phases are explored by tuning alloying and process parameters and environments. In this work, the co-precipitation kinetics of Cu-rich precipitates (CRPs) and Ni(Al, Mn) under Mo alloying and high magnetic field (HMF) heat treatment are studied by integrating computational thermodynamics and kinetics, together with advanced characterization. The results suggest that the Mo alloying accelerates the precipitation kinetics of Cu precipitates through changing solubility and diffusivities of Cu atoms. The contributions of HMF are mainly related to the magnetic Gibbs free energy, which alters thermodynamics and kinetics of precipitation. Through combining Mo alloying and HMF heat treatment, multiple phases and hierarchical precipitation are achieved to develop high-performance steels.