When a train travels through tunnel at a high speed, large pressure variations are produced on the train surface by pressure waves. In particular, when an express train travels through a narrow tunnel at a speed higher than that of a conventional train, more severe pressure variations can occur and cause passengers ear discomfort. This paper presents a very simple and effective reduction method of the large pressure variation for a narrow conventional tunnel. When a compression wave and an expansion wave are superposed, the pressure variation can be greatly reduced. Using this phenomenon, this study proposes the construction of a dummy tunnel duct which superposes the pressure waves and reduces the large pressure variation. Using the proposed method, the construction cost is much lower compared to other methods because the dummy tunnel duct can be constructed at the entrance or at the exit of an existing tunnel with a simple tunnel shape. To investigate the change in the maximum pressure difference and pressure variation ratio with the application of a dummy tunnel duct, full-scale tests and numerical analyses were conducted. The results showed that the maximum pressure changes and pressure variation ratio are significantly reduced by a short dummy tunnel duct. From these results, the dummy tunnel duct is expected to be a very economical and practical solution to passenger ear discomfort problems for express trains traveling through conventional narrow tunnels.