Unconscious design can arouse users' affinity for new things, thus realizing effective communication between users and design. The work aims to observe the unconscious standing position selection behavior of subway passengers, and study the layout of lumbar support in the carriage, so as to alleviate the lumbar pressure of standing passengers while effectively utilizing the internal space of the subway. Firstly, the concepts of "unconscious" and "unconscious design" were summarized. Secondly, the explicit needs of passengers were obtained through questionnaire surveys and user interviews to confirm the necessity of the lumbar support study. Thirdly, the unconscious standing position selection behaviors of passengers were observed and the causes were analyzed, to obtain the implicit needs of passengers and verify the feasibility and reasonableness of the lumbar support layout from the perspective of ergonomics. Lastly, the design principles of lumbar support in the subway were summarized to carry out design practice. The lumbar support layout design based on the unconscious concept in the subway can better serve the passengers, not only improving the experience of standing passengers, but also bringing guiding significance to the application of subway lumbar support design in the future.