Choice overload, which means that large assortment may have negative effect on people’ s decisions and behaviors, has already been tested in many different research papers (Iyengar & Lepper, 2000; Chernev, 2003; Gourville & Soman, 2005). However, when and how choice overload affect people’s behavior still remains open, which makes it valuable for us to study the effect of large assortment in a more comprehensive scenario. In this research, I test how the assortment size affect choice overload in a scenario including four related factors: choice set complexity, decision task difficulty, preference uncertainty, and decision goal. The purpose of the research is to study the effect of all the four moderators and assortment size on choice overload in a single comparable situation, which allow us to model the decision-making scenario in the real life and test the basic and interaction effect of those factors.