Systematic results of the photoemission spectra for different core levels such as, Tm 4p, 5p and 3d in the mixed valent Tm-monochalcogenides (TmS, TmSe and TmTe) obtained by both experimentally and theoretically are reported. The effects of the electron-electron correlation due to the interaction between core-holes and 4f-electrons or the interaction between different configurations are considered to explain the spectral features, depending on the principal (n) and orbital quantum numbers of the core levels. Any sharp peak corresponding to a spin-orbital term is not observed especially from the n = 4 states. Instead, the multiplet structures are dominantly observed, and the physical identity of the spin-orbital peaks is totally or partially dissolved into the multiplets. Moreover, the electron-correlation effect is found to be dependent on the valence components (Tm2+ and Tm3+). In the case of the Tm 4p core level, in which the principal quantum number is identical with the valence 4 f, the correlation effect is stronger, and the configuration interaction is therefore considered to explain the spectral features. The photoemission spectra for the shallow core level Tm 5p also show the effect of electron correlation, but weaker than that for Tm 4p. This has been confirmed by the resonant photoemission spectroscopy taken at Tm 4d-4f absorption edges. In addition, the feature of Tm 3d photoemission spectra is discussed. All the experimental spectra are compared with the calculated ones. It is therefore understood that the electron correlation effect plays an important role on determining the various features in Tm 4p, 5p and 3d photoemission spectra.