12　cobalt　porphyrin　catalysts　were　designed　and　synthesized,　and　their　catalytic　activities　for　oxidation　of　p-nitrotoluene　(PNT)　to　p-nitrobenzoic　acid　(PNBA)　were　investigated　in　the　presence　of　molecular　oxygen　under　mild　conditions　(55　degreesC,　2.0　MPa).　It　was　found　that　the　12　cobalt　porphyrins　had　consider-able　catalytic　activity　for　the　reaction.　The　correlation　between　molecular　frontier　orbital　energies　of　all　the　cobalt　porphyrins.　and　their　catalytic　activities　was　investigated　by　means　of　the　PM3　semi-empirical　molecular　orbital　method,　and　the　result　presented　that　the　catalytic　activity　of　4-coordination　or　5-coordination　of　cobalt　porphyrins　was　related　with　E-HOMO　and　DeltaE(L-H),　had　greater　impact　on　catalytic　activity　than　E-HOMO　and　the　lower　the　E-HOMO　and　DeltaE(L-H),　the　higher　the　catalytic　activity.