The present invention relates to a chromatography analysis method and a system employing the same which are capable of automatically determining an constituents to be detected contained in the unknown sample based on results on measuring a standard sample. The standard sample is first separated to obtain its chromatogram. The system extracts the necessary information from the chromatogram to identify the peaks corresponding to the constituents to be detected to set widths of time windows for the peaks. Then, the time windows thus set are applied to the chromatograms obtained by the separation of the unknown sample to identify the constituents contained in the unknown sample. By employing the present invention, it is unnecessary for an operator to input the retention time of each constituent to the system.