Abstract: Stiffened Deep Mixed(SDM)column is a new kind of composite material column. It is formed by inserting a precast concrete core pile into the center of a Deep Mixed(DM)column immediately after the construction of deep mixing column. This new composite column is appropriate to reinforce the thick soft soil. However, previous studies have been mostly focused on the performance of SDM column under rigid foundation. There have been few studies regarding its mechanical behavior under flexible load at present. This paper presents a numerical study to investigate the behavior of SDM column-supported embankment over soft soil. Firstly, a comparison of results by the numerical model and field data was conducted to verify the reliability of the numerical model. Based on the calibrated numerical model, the study was conducted to investigate the influence factors of ratio of concrete core pile length to DM column length, area ratio of concrete core pile and column spacing on the behavior of SDM column-supported embankment over soft soil. The results showed that the settlement could be effectively reduced and the pile efficacy could be increased to some extent by increasing the ratio of core length to DM column length, and reducing column spacing. The results have the practical values to guide the application of SDM columns in practice.