The goal of material chemistry is to study the relationship among hierarchical structure, chemical reaction and precision preparation for materials, yet tracking pyrolysis process on multi-dimensional scale is still at primary stage. Here we propose packing mode analysis to understand evolution process in high temperature reaction. As a proof of concept, we first design a salan-ligated Mn₃ (Mn₃(3-MeOsalophen)₂(Cl)₂) cluster and pyrolyze it under an inert atmosphere directly to a mixed valence MnO_x embedded in a porous N-doped carbon skeleton (MnO_x/C). Meanwhile, combining thermogravimetry-mass spectrometry (TG-MS) with other characterization techniques, its pyrolysis process is precisely tracked real-time and Mn²⁺/Mn³⁺ ratios in the resulting materials are deduced, ensuring excellent electrochemical advantages. As a result, the as-preferred MnO_x/C-900 sample reaches 943 F/g at 1 A/g, maintaining good durability under 5, 000 cycles with 90% retention. The highlight of packing mode analysis strategy in this work would provide a favorable approach to explore the potential relationship between structure and performance in the future.