Abstract: The peaty soil foundation has notable post-construction settlement due to long-term loading. Based on the test results, the secondary consolidation properties of peaty soil from Kunming and Dali cities are studied, and some influencing factors of the secondary consolidation coefficients (C_α), such as the depth of sampling, consolidation pressure (p), loading ratio (R) and loading method, are discussed. The results show that the curve of e-lgt is mainly reverse "S", and the secondary consolidation deformation has relatively high percentage in the total compressive deformation. The secondary consolidation coefficient (C_α) of peaty soil increases with the increasing consolidation pressure to the peak value, then decreases slowly and stably. But the consolidation pressure corresponding to the peak value of C_α, is about 100~200 kPa, does not agree with the preconsolidation pressure (p_c). The mechanism of the secondary consolidation is analyzed by establishing the micro-structure models for peaty soil. A conclusion is drawn that the peak value of consolidation pressure is the critical load which generates peaty soil changing from porous to tight state. Moreover, there is a significant correlativity between the coefficient of secondary consolidation and the compression index, and the C_α/C_c ratio is almost a constant value, which is consistent with the values reported in the literatures for similar soils.