In order to identify the best design principles of flashlight, the paper uses the design elements, and the use experiences of professionals to do assessment survey. The purpose is to understand the users’ needs for the flashlight product awareness, and by using the order of design element importance of assessment results, it is possible to provide a value for new flashlight product design and application. At the same time, it can achieve a balance between human beings and items. First of all, method of Typological model is used to sort the design structure to functional, shape, usage and overall design considerations, and they are used as views of assessment. Next, Grey Relational Analysis is applied to analyze the ordering of flashlight importance design. The result is shown by using Grey Structure Model, and it also provides the best design strategy of flashlight design application. Finally, the paper not only helps designers sort out the scientific basis for the design in complicated design structure, but also convey the actual needs of users.