The problem of determining and understanding the role of tip electronic states is one of the central and critical scietific problems in scanning tunneling microscopy (STM) and spectroscopy (STS). In this paper, we described a theory and a practical method for in-situ characterization of the tip electronic states. The method consists of a deconvolution procedure, from which the density of states (DOS) of the tip is recovered from the measured tunneling spectra. The tip DOS, obtained from deconvolving an experimental tunneling spectrum, can be compared with predictions of first-principle numerical calculations of various realistic tip structures, or independent measurements, for example, field emission spectroscopy and photoemission spectroscopy. The reference tunneling spectrum of the sample can be obtained using a flat-DOS blunt tip, for example, following the tip-treatment process described by Feenstra et al. Using the deconvolution method, we analyzed the STM and STS data published by Pelz. The results indicates that the W tip picked up a Si cluster in the middle of a scan on a Si sample. To further clarify the role of tip electronic states in STM imaging process, a set of new experiments is proposed. © 1992.