Soil samples from a long-term spot experiment (17 years) with different treatments were used for studying the oxidation stability of soil organic matter and humic acid fractions by the alcohol precipitation technique, and the optical properties of humic acid and its fractions. Types of humic acid and its fractions were also classified. With applying organic materials (compost or corn straw) for a long time, soil organic matter content increased obviously, its oxidation stabilily decreased; the distribution center of soil humic acid fractions moved to the fraction precipitated by alcohol with a high concentration, and the proportion of fractions with a smaller partical size rose; E₄ and E₆ values of humic acid decreased and E₄/E₆ increased. Application of chemical fertilizer resulted in a contrary result.