Density　functional　theory　calculations　have　been　performed　to　reveal　the　regioselective　[2　+　2]　and　[3　+　2]　photocycloaddition　of　ethyl　3-carboxylate-1,4-diphenyl-1,4-dihydropyridine　affected　by　the　irradiation　wavelengths.　It　was　found　that　the　regioselectivity　is　affected　by　irradiation　wavelength,　resulting　in　the　formation　of　the　parallel　cage　dimer　diazateraasteranes　by　[2　+　2]　cycloaddition　and　the　orthogonal　cage　dimer　diazatetrakishomocubanes　by　[3　+　2]　cycloaddition.　The　difference　in　product　formation　can　be　attributed　to　the　distinct　mechanism　revealed　by　the　DFT/TDDFT　analysis　at　the　PCM/M06-2X/def-TZVP//B3LYP/6-31g(d)　calculation　level.　The　[2　+　2]　photocycloaddition　has　two　steps　including　an　intermolecular　and　an　intramolecular　[2　+　2]　photocycloaddition,　and　the　[3　+　2]　photocycloaddition　has　three　steps　including　the　sigma　bond　formation,　the　sigma　bond　free　rotation　and　intramolecular　reaction.　Both　the　intramolecular　reactions　of　[2　+　2]　and　[3　+　2]　photocycloaddition　have　the　second　excitation　process　of　the　key　intermediates　which　is　related　to　the　irradiation　wavelengths　and　the　regioselectivity　of　the　photocycloaddition　products.