Based on the "clear adaptation" distance of driver at the tunnel exit, the factors of the identification distance and the complete reading mark at the interchange exit are only considered. The minimum spacing of the tunnel exit and interchange exit under the condition of the different lane numbers and design speeds is briefly analyzed and demonstrated. At the same time, based on Songshugang Tunnel in Jinbeidou - Niulandang Section Reconstruction Project in Wenzhou National Highway 235 and its interchange exit, the design spacing of Songshugang Tunnel Exit and the interchange exit is inspected. The relevant safeguard measures are proposed for the practical conditions of the project.