Currently, the GIS-based multiple-criteria decision making(GIS-MCDM) for single-objective is generally used for spatial suitability evaluation, but the way of selecting objectives is overly subjective, because there is no function to compare objectives before selecting them. Based on the research results about GIS-MCDM method in the past 30 years, this paper proposes a GIS-MCDM approach for dual-objectives that can be effectively combined with ArcGIS software. In comparison with MCDM for single-objective, our method adds a function of objective decision-making, which makes spatial suitability evaluation be able to deal with conflicting objectives. Our study establishes a systematic procedure for decision space approach, which is the core of dual-objective decision making. Moreover, a new way of partitioning conflict region on decision space is introduced. This approach keeps the ratio of the area to conflict region assigned to the objectives equal to the ratio of the weights assigned to the objectives when partitioning the conflict region. Finally, a case study of Baishan Town in Beijing is used to examine and illustrate the dual-objective decision-making method.