In　this　paper,　we　present　a　theoretical　investigation　of　multiphoton　processes　between　a　single　atom　and　a　multimode　optical　or　microwave　field.　At　first,　we　examine　two-photon　excitation,　which　involves　the　simultaneous　excitation　of　two　photons　in　different　cavity　modes　by　a　single　atom.　We　demonstrate　that　when　the　transition　frequency　of　an　atom　is　equal　to　the　sum　of　the　frequencies　of　two　cavity　modes,　there　exists　a　resonant　coupling　between　the　atom　and　the　two-mode　cavity　field,　which　leads　to　the　simultaneous　excitation　of　the　two　cavity　photons　with　the　atom　initially　in　its　excited　state.　Moreover,　we　found　that　this　coupling　is　coherent　and　reversible,　allowing　the　atom　initially　in　the　ground　state　to　simultaneously　absorb　all　the　photons　from　the　cavities　and　transit　to　its　excited　state.　Finally,　we　also　show　that　this　coherent　interaction,　in　principle,　can　be　extended　to　describe　multiphoton　processes　between　a　single　atom　and　a　multimode　cavity　field,　such　as　a　three-mode　cavity.　The　parameters　used　in　the　numerical　simulation　are　based　on　the　experimentally　demonstrated　values　in　circuit　quantum　electrodynamics　systems.