This study was performed to identify the theoretical attribution of project type that moderates the impact of project delivery systems on cost performance. Previous studies have used direct relationship analysis to evaluate the project performance (e.g., the relationship between PDS and its cost performance, or the relationship between project type and cost performance). These analyses can cause inconsistent results and need to be analyzed in a single model. To combine the relationships between influential factors on cost performance, a causal model (i.e., moderation model) was suggested. The objective of this study is to develop a moderation model and test the statistical significance of moderation effect between PDS and cost performance. As a preliminary study, we established a simple moderation model and examine the moderation effect of project type. To test the model, 134 public sector projects completed between 1998 and 2013 in South Korea were utilized. The dataset consists of both Design-Build and Design-Bid-Build projects which are the most prevalent delivery systems. Even though the preliminary test results were not statistically significant, we can suggest the better way to understand the causal relationship moderated by project type between PDSs and their cost performance. This study is expected to provide the theoretical basis of the mechanism by which PDS impact cost performance, help project participants to select PDS by considering moderating effects in specific project types, and evaluate PDS appropriately in terms of cost performance.