In order to determine the best inoculation methods of compound microorganisms in solid waste composting, dissolved organic matter (DOM) during the process of composting under five different inoculation methods, including inoculation at the start, at the high-temperature phase, after the high-temperature phase, at the maturity phase and without inoculation, was tested through spectral analysis to investigate the time variations of DOM components in solid waste composting. Fluorescence spectra analysis of DOM indicated that the spectral characteristics of DOM in the composting piles of the five treatments exhibited a certain trend with composting time increasing, in which macromolecules with complex structures and humic substances gradually increased, and the heap materials became more and more stabilized. According to the comparisons of the fluorescence spectroscopy maps and related parameters, the treatment of inoculating compound microorganisms at the start time or after the high-temperature phase could notably speed up the humification process in solid waste composting.