The modern infrared spectroscopy (FT-IR) is a rapid and direct method with high signal-to-noise ratio and good repeatability to analyze the complicated mixture systems such as food, Chinese herbal medicine. Second derivative infrared spectroscopy (SDIR) can be used to handle severely overlapped spectra and enhance the apparent resolution. If the differences in FT-IR and SD-IR spectra are too small to tell, two-dimensional correlation infrared spectroscopy (2DCOS-IR) can be employed to unfold FT-IR spectra in a second dimension to identify the differences more remarkably and convincingly.With the holistic analytical method, ‘‘Tri-step infrared spectroscopy’’ (FT-IR combined with SD-IR and 2DCOS-IR), the extensive and exact analysis and identification of complicated mixture systems can be achieved.