This paper studies two important factors of the location of new facilities of the chain-companies: the allocation of market share and service radius of facilities.Considering the spatial customer choice,we use step utility function to construct a new model of a chain-company's new facilities location in competitive environment based on the fact that the utility function is an important factor of the allocation of market share of facilities in a competitive environment.Both the decay cover and the service radius of facilities are considered in the model.The genetic algorithm to solve this model is developed and computational experiment is described.The result shows that this model and algorithm is suitable for the location decision of the chain-company's new facilities,and could efficiently obtain an approximate solution.