In this study, soil samples under long term OW treatments were collected to analyze the changes in soil humic acid composition. The treatments in this study included a control (CK), fodder grass (FG), mushroom (MR), maize straw (MS) and tree leaves (TL) wastes. Soil HA structure was analyzed using (FTIR) and (¹³C- NMR). The results from the study showed that treatments TL, MS, FG, and MR increased soil organic carbon (SOC) by 23.45%, 13.83%, 11.90%, and 5.76%, respectively. Similarly, the contents of humic carbon (HAC) increased in all the OW treatments. Moreover, there was a positive relationship between O-alkyl C and SOC, alkyl C, soil HA contents while a negative relationship was observed between O-alkyl C and aromatic C, and carbonyl C. Compared with other treatments, TL and FG were also recorded as having the lowest E4/E6 ratio, ΔlogK value, and hydrophobic carbon (C)/hydrophilic carbon (C) ratio of soil HA. In conclusion, the OW treatments improved the structural characteristics of soil humic acid where the most effective treatment was TL as it higher the accumulation of SOC, soil HA, and made the structure of HA more complex and stable.