In order to study the mechanical properties of stabilized peaty soil, a series of stabilization tests were carried out with machine-made sand as filling material, cement and phosphogypsum as cementing material. Based on the unconfined compressive stength test and uniaxial cyclic loading and unloading test, the stabilized effect of peaty soil was discussed under the different content of cement and phosphogypsum. According to the damage theory and the strain equivalence hypothesis, an elasto-plastic damage model of stabilized peaty soil was established under uniaxial compression. The results show that the compressive strength of stabilized peaty soil increases with the increase of cement content, and the strength growth rate increases first and then decreases with the increase of phosphogypsum content. The stress-strain hysteretic curve of stabilized peaty soil presents a crescent shape with unclosed bottom, and the unclosed areas of hysteretic curve at the beginning of plasticity and near failure stages are larger than that of other cycles, which indicates that more energy loss occurs in these two stages. Finally, considering the effects of cement content and phosphogypsum content, the parameters of the elasto-plastic damage constitutive model of stabilized peaty soil are obtained by curve fitting method according to the test results.