This paper presents a numerical simulation of a full scale test of a cement-treated soil column under a cantilever condition in a field. A three-dimensional finite element analysis was performed to verify that a elasto-plastic model proposed by the authors can simulate the bending failure behaviour of the full scale soil-cement column. The elasto-plastic model can describe the tensile softening behaviour of cement treated soils. The numerical results agreed reasonably with the experimental results, indicating that the elasto-plastic model is suitable for describing the full scale bending behaviour of the cement treated soil. Moreover, the size effect on bending tensile strength of cement treated soils was discussed by comparing the full scale and laboratory test results. For the small specimen, the bending tensile strength was much larger than the tensile strength. On the other hand, for the full scale specimen, the bending tensile strength was roughly equivalent to the tensile strength. It was found that the main reason for the size effect on bending tensile strength lay on the ratio of the softening zone size to the specimen size.