The purpose of this study is to identify the occurrence of Sudden Moments of Inspiration (SMI) in the sketching process of industrial design through experiments to explain the effect of sub consciousness on SMI. There are a pre-experiment and a formal experiment. In the formal experiment, nine undergraduates majoring in industrial design with same education experience were selected to receive a design task. In the task, nine undergraduates were divided into three groups randomly by lot. While two groups received A or B subliminal suggestions through a slide picture presentation, the other one group was not. The design processes and sketches of the three groups were recorded and analyzed, using concurrent and scientifically experimental methods such as real-time videos and protocol interviews. Comparison of the three experiments provided convincing evidences of the effect of sub consciousness on SMI in the sketching process of industrial design.