In this paper a similarity theory is carried out, which is suitable to both sedimenthyperconcentration and sediment-lowconcentration flow. And crucial technolegy how to engage in sediment-model experiment is carried out too. According to the similarity laws,a sediment transport model is designed for Xiaolangdi Project. All model scales are given out in the paper. The results of the model experiment explain that the model designed on the basic of this similar theory is similar in the main to the prototype in all aspects such as the currents,sediment movements,the density currents,the location and quantity of scouring and deposition and the grain size of sand in the river channel.