Deep　understanding　of　the　rate-limiting　step　in　the　oxidation　process　of　cyclohexane　to　adipic　acid　would　be　useful　for　improving　the　activity　of　catalysts　and　selectivity　of　goal　products.　The　rate-limiting　step　lied　in　high-valent　species　generation　or　C-H　bond　oxidation　remains　a　controversial　topic.　In　this　paper,　the　mechanism　of　high-valent　species　generation　and　C-H　bond　activation　was　investigated　by　density　functional　theory.　It　was　observed　that　the　activation　barrier　of　the　high-valent　species　was　lower　than　that　of　C-H　bond　activation;　thereby　the　C-H　bond　oxidation　was　determined　as　the　rate-limiting　step.　Calculated　geometries　and　energies　were　in　close　agreement　with　the　experimental　observations.　Furthermore,　frontier　molecular　orbital　analysis　revealed　that　the　C-H　bond　interacted　with　the　high-valent　species　in　different　orientation　and　it　showed　how　the　reaction　was　manipulated　and　controlled　by　the　iron-porphyrin　in　the　catalytic　process.　Given　the　calculation　correction,　experiments　were　designed　to　reveal　the　rate-limiting　step.　This　work　provides　a　clear　view　of　the　debut　on　the　rate-limiting　step　of　the　alkane　oxidation.　It　should　be　a　significant　step　forward　for　understanding　the　relationship　between　the　porphyrin　molecular　structures　and　catalytic　activity　accurately　and　for　predicting　and　designing　high-activity　catalysts.