Spinodal decomposition has been widely studied in binary or ternary material systems but rarely in multicomponent systems. Here we propose a strategy to manipulate the spinodal decomposition behavior in a typical Ti-Zr-C-N-Ni cermet system based on the Gibbs free energy and its second derivative of Fcc-(Ti, Zr)(C, N) phase. The impact of constituents and temperature on miscibility gap and spinodal decomposition was visualized. Interestingly, Ni impeded the spinodal decomposition of this system, while N had a complex effect. Furthermore, a subtle increase in Ni content (by 0.5 at.%) counteracted the effect of 20 at.% N addition at 1500 °C. The calculated results are further supported by the microstructure analysis of (Ti, Zr)(C, N)-Ni samples. The adopted strategy presented herein enables the optimization of cermet constituents and heat-treated temperature to manipulate the spinodal decomposition behavior for designing high-performance multicomponent materials.