A　new　method　of　complex　complete　quadratic　combination　with　three　components　(CCQC3)　for　non-classically　damped　irregular　structures　is　proposed　in　this　paper,　in　which　both　modal　displacement-velocity　and　velocity　correlation　coefficients　are　involved　along　with　the　modal　displacement　correlation　coefficients　in　the　normal　CQC3　formula.　Moreover,　the　effect　of　the　seismic　incident　angle　on　the　structural　response　is　considered;　and　formulas　for　the　critical　angle　and　the　corresponding　critical　response　are　given.　The　new　CCQC3　formula　is　as　concise　as　that　of　the　CQC3　method　and　has　explicitly　physical　meaning.　If　the　correlations　among　modal　responses　are　ignored,　the　CCQC3　method　is　reduced　to　the　method　of　complex　square　root　of　the　sum　of　squares　with　three　components　(CSRSS3).　Analytical　examples　are　presented　in　the　paper　to　compare　the　validity　between　CCQC3　and　CSRSS3　methods.　Meanwhile,　time　history　analyses　of　structures　subjected　to　artificial　earthquake　waves　which　are　synthesized　from　design　spectra　are　carried　out　to　verify　the　complex　mode　superposition　method.　The　results　illustrate　that　the　CCQC3　method　is　more　accurate　and　suitable　for　seismic　response　analysis　of　important　structures;　however,　the　CSRSS3　method　may　be　adopted　for　general　structures　in　order　to　simplify　the　calculation.