The aim of this study is to investigate the effect of Ca-bentonite (CB) on organic matter transformation during pig manure (PM) composting. In this paper, five treatments representing different CB concentrations(0%CB, 2.5%CB, 5%CB, 7.5%CB and 10%CB of dry PM weight basis) were mixed with initial feed stock composting system. Moreover, various spectroscopic approaches like UV-Vis spectra, fluorescencespectra (FS) and FTIR were used to characterize the evolution of water-extractable organic matter transformation during PM composting. In addition, on the basis of spectroscopic characterization, multivariate statistical analysis was performed to investigate the correction among the different parameters related to organic matter transformation. The results showed that the concentration of DOC decreased along with the increase of CB dosage during the PM composting, and among all the treatments the degradation rate of DOC concentration was 49.11%~62.92%. Meanwhile, it was observed from spectra results that the peak intensity of humic substance increased and the position was red shift during composting. As compost ended, the SUVA254, SUVA280 and the amount of increase related to humification coefficient (λ) of all treatments were higher than control, the amount of increase were 16.51%~47.72%, 8.58%~44.02% and 23.16%~88.22% in order, and the maximum was observed in 5%CB applied treatment. And FTIR spectra revealed the same result. The correlation analysis showed that SUVA254 reflected the change of compost maturity best in all spectral parameters studied in this paper. Overall, the results indicated that adding 5%CB considerably enhanced the organic matter degradation and the humification during PM composting.