Abstract:Beidou system has been briefly introduced in this paper, basic concept of undifferenced relative positioning has been discussed, and the principle for establishing undifferenced relative positioning model has been introduced in detail. The detailed process for establishing the function and stochastic model of single epoch undifferenced relative positioning model have been introduced. By using LAMBDA method, single ambiguity fix has been realized. The positioning accuracy of the baseline solution by using single epoch relative model has been analyzed as well.