The influence of municipal landfill age on the characteristics of humic substances in leachate on the basis of investigating 12 different kinds of leachates from landfills in Fujian province is presented in this study. It was shown that the concentration and percentage of fulvic acid (FA) were obviously higher than those of humic acid (HA). As the landfill age increased, the concentrations of HA, FA and humic substances (HS) increased, moreover, the percentage of HA first increased and then decreased. While the percentages of FA and HS first increased and then fluctuated with the landfill age. The UV-Vis analytical results of HA and FA through E280, E300/E400 and E465/E665 revealed that HA had a relatively higher content of aromatic compounds and higher molecular weight than FA. The humification of FA had a tendency to increase as the landfill age increased, while HA had opposite result. The E300/E400 and E465/E665 of HA and FA fluctuated with increasing landfill age. A mathematical model simulating the concentration of humic substances varied with the landfill age was presented and demonstrated based on degradation kinetics. The simulated results were close to the measured values with a correlation coefficient R2 of 0.820, 0.932 and 0.946, respectively, indicating that the concentrations of HA, FA and HS could be accurately forecasted.