Packaging design is one of the most important visual representations of low-fat foods and is a key factor in the perception of the health of the product. The complexity of packaging induces the automatic processing of relevant concepts by consumers, which affects their attitudes; however, this process is not well understood. We developed a sequential mediation model based on the theories of conceptual fluency and conceptual metaphor to examine the impact of packaging complexity on consumers’ purchase intentions. In this study, 353 volunteers were recruited to participate, and variables were measured using questionnaires on packaging intention, brand complexity, concept fluency, and brand attitude. The results indicated that it was simple to increase consumers’ conceptual fluency and brand attitude; conceptual fluency had a significant predictive effect on brand attitude and purchase intention; brand attitude had a significant predictive effect on purchase intention and conceptual fluency; and brand attitude served as a mediator between packaging complexity and purchase intention. This study demonstrated that the general characteristics of packaging design could influence consumers’ purchase intentions and provide direction for the packaging design of low-fat foods. In addition, we examine the study’s theoretical and practical implications.