Vodyanitsky method was applied to calculate the effect of pig manure application on thermodynamic parameters of humic acid (HA) and fulvic acid (FA) in brown soil. The results showed that the formation of HA, FA was spontaneous and exothermic reaction. Compared to HA, the energy state of FA was low, but its order degree and thermal stability were high. The formation rate of FA was faster than that of HA. After the application of pig manure, the energy state, order degree and thermal stability of HA, FA all declined. And the changes of thermodynamic parameters were related to that of elemental compositions of HA and FA.