The usage of fly ash in constructing expressway is more and more extensive and the technology of constructing is becoming to more and more mature. But the stability and failure mode of the embankment is lack of researches. In order to study the stability and failure mode of the embankment, the plan for the study of the static model test of light fly ash embankment was designed, in which the model material was selected based on the similarity principle of the model test. The mechanical characteristic under static load is simulated. The internal force, the relationship between the stress and load, the displacement and load of different depth of the embankment were obtained through the test. The deformation and mechanical characteristic is studied and the influence of concrete pavement is also considered. The experimental results show that the high filling subgrade has an excellent stability and high bearing capacity and the influence of the concrete pavement is relatively large.