A　real　value　form　formula　of　complex　mode　response　superposition　method,　which　is　based　on　the　stationary　random　vibration　theory　and　seismic　design　spectra,　is　derived　to　analysis　the　non-classically　damped　linear　system.　This　formula　includes　new　modal　velocity　correlation　coefficient　and　displacement-velocity　cross　correlation　coefficients　besides　the　modal　displacement　correlation　coefficient　in　normal　Complete　Quadratic　Combination　(CQC)　formula.　Moreover,　the　new　method　has　same　accuracy　and　concision　as　normal　CQC　method　because　there　is　no　further　assumption　involved　in　it　except　that　have　been　adopted　in　normal　CQC　method.　The　new　proposed　CCQC　method　is　easy　to　master　and　apply　for　design　engineers.　The　example　analyses　and　the　numerical　comparisons　with　CCQC　method,　CSRSS　method,　and　the　forced　uncoupling　method　proposed　by　seismic　design　code　are　carried　out.　The　results　are　verified　by　those　obtained　from　the　step-by-step　integration　method　under　the　simulated　man-made　seismic　wave　input.　The　results　demonstrated　that　CCQC　method　based　on　design　spectra　is　more　accurate　than　CSRSS　method.　Meanwhile,　the　forced　mode　uncoupling　method　widely　used　in　seismic　design　code　also　has　good　approximation,　even　though　the　relatively　simple　example　structure　is　strongly　non-proportional.