To　address　the　limitations　of　traditional　complete　quadratic　combination　(CQC)　modal　combination　coefficients　in　calculating　ground　motions　with　narrow　bandwidth　and　long　periods,　a　revised　methodology　is　proposed.　The　new　CQC　modal　combination　coefficients　are　formulated　by　considering　the　spectral　characteristics　of　strong　ground　motion,　taking　the　modified　Kanai-Tajimi　spectrum　model　as　a　prerequisite,　and　applying　random　vibration　theory.　Simultaneously,　a　random　phase　simple　harmonic　process　model　for　a　single　harmonic　component　is　established,　and　corresponding　combination　coefficients　are　provided.　The　necessity　and　rationality　of　considering　the　spectral　characteristics　of　strong　ground　motion　are　demonstrated　from　three　perspectives:　differences　in　power　spectral　models,　variations　in　combination　coefficients,　and　the　inherent　combination　mechanism.　As　an　illustrative　example,　the　layer　shear　model　is　analyzed　and　compared　with　the　results　of　the　structure＇s　modal　combination　taking　different　combination　coefficients.　This　comparison　is　conducted　under　the　influence　of　long-period　simple　harmonic　waves,　four　natural　seismic　waves　in　the　basin,　and　the　50　natural　ground　motions　suggested　by　ATC-63,　respectively.　The　results　indicate　that　the　modal　combination　coefficients　developed　by　considering　the　spectral　characteristics　of　strong　ground　motions　are　more　reasonable　and　can　serve　as　a　viable　replacement　for　traditional　CQC　combination　rules.　This　is　especially　advantageous　when　dealing　with　ground　motion　inputs　characterized　by　narrow　bandwidth　and　long　periods,　providing　significant　benefits　in　such　scenarios.　©　2024