The　assumption　and　problem　of　the　mode-superposition　response　spectrum　method　in　seismic　design　code　is　discussed　based　on　a　brief　review　of　the　development　of　the　seismic　design　method　for　building　structures.　The　scope　of　application　for　the　classical　damping　theory　is　analyzed　and　the　necessity　of　the　research　on　mode-superposition　method　for　non-classical　damping　is　presented.　The　progresses　on　the　mode　superposition　response　spectrum　theory　are　discussed.　This　includes:　1)　the　complex　mode　superposition　method　(in　real　form)　for　the　non-classically　damped　linear　system　and　the　general　calculation　formula　for　the　application　of　code;　2)　the　complex　complete　quadratic　combination　(CCQC)　method　for　the　non-classically　damped　linear　system,　which　is　based　on　the　same　assumptions　as　in　deducing　the　complete　quadratic　combination　(CQC)　method　which　is　popularly　used　in　seismic　design　codes　of　many　countries;　3)　the　complex　complete　quadratic　combination　with　three　components　(CCQC3)　method,　which　is　a　generalization　of　the　CCQC　method　to　the　case　of　multi-components　and　multiple-support　seismic　excitations　and　deducing　corresponding　method;　4)　the　approach　for　calculation　of　seismic　response　of　the　non-classically　damped　system　with　overcritical　damping　and　the　calculation　method　of　seismic　response　for　the　linear　system　with　multiple　eigenvalues;　5)　the　time-dependent　CCQC(t)　algorithm　considering　non-stationary　earthquake　ground　motion;　6)　an　applied　and　effective　method　to　solve　the　low　order　complex　vector　basis　for　the　large　linear　non-classically　damped　system,　which　can　be　expediently　used　in　practice　to　avoid　the　unknown　errors　coming　from　the　forced　uncoupling　method;　7)　bringing　forward　the　concept　of　partial　quadratic　combination　in　order　to　reduce　the　calculation　amount　of　CQC　and　CCQC　methods,　and　studying　the　primary　estimation-criterion.　The　reasonability　and　applicable　scope　of　these　methods　are　also　briefly　discussed　in　this　paper.　©　Higher　Education　Press　2007.