An on-line operation of micro-spectrometer and liquid drop analyzer is proposed in this paper. Comparing with a full spectral range spectrometer system, a micro-spectrometer has narrow spectral range that results in its inefficiency or inability in qualitative analysis of a mixed liquid since more than one function group of the mixed liquid might cause a peak or valley in the spectrogram at almost the same wavelength. A liquid drop analyzer (LDA) is an instrument that detects the characters of a liquid by monitoring its drop forming process. The LDA gives a fingerprint that is unique for certain liquid due to its specific chemical, physical and mechanical characters. An approach of combining micro-spectrometer with a fiber drop analyzer, by which a virtual 3D liquid fingerprint is formed, is described and it functions like a full range spectrum. The signals obtained from the micro-spectrometer and liquid drop analyzer, the method of on-line operation and database setting up, the experimental device and test results are described and discussed in the paper.