Engineering design is a complex decision-making process which frames the transition from an engineering problem to a final product, to meet a set of requirements. During this process, perception is inevitably involved. Perception, a term originated from psychology, referring to a process where a person arrives at an interpretation of his/her sensory experience about the surroundings, has been involved in a broad scope in engineering design, e.g., understanding a design problem, comprehending customers requirements, conceptualizing design thoughts, organizing and managing resources, and evaluating alternative solutions. To study the engineering process from the perception’s perspective, a theoretical model has been proposed. In this model, workload, skill, knowledge, and affect are chosen as major factors. Based on the model and the Environment-Based Design methodology, methods are proposed to quantify designer’s perception and performance at conceptual design stage. Experimental studies have been conducted to validate the proposed model. As a result, the model serves well as a phase-based quantification tool for designer’s perception and performance. In addition, a significant positive correlation has been found between one’s perception and performance. Furthermore, the model implies a foundation to improve one’s performance for engineering design.