Abstract: This paper proposed a systematic optimizing method for the composi-tion of multicomponent mobile phase in high performance liquid chromatography. A newchromatographic response function (CRF) has been constructed according to the funda-mental retention equation and rule of peak width at half-height, and theoptimalcomposition of multicomponent mobile phase can be automatically predicted by acomputer with CRF. This paper improved the known complex method, therefore, theoptimal mobile phase composition in the global area may be found by means of this modi-fied complex method. The optimal separation conditions of four vitamins and threenitrophenols were determined by use of the optimizing method reported in this paper. Theresults predicted by the computer were verified by the experimental data obtained inHPLC using ternary mobile phase.