In order to solve the problem of excessive water pressure during tunnel operation caused by the insufficiency of conventional drainage system in road tunnels, a new three-way drainage system was proposed and designed, with a one-way valve in the center of the elevated arch to carry out drainage, and a model test group was designed to validate the pressure-reducing performance, and a theoretical derivation was carried out according to the experimental law in reverse to investigate the pressure-reducing law of the new three-way drainage system and its applicability. The designed drainage system was a kind of three-way drainage system that can "point-to-point" drain the tunnel to reduce pressure, which consisted of conventional longitudinal and circumferential blind drainage pipes and one-way valve channel designed at the upward arch. From the results of the model test, the three-way drainage system can effectively alleviate the drainage pressure of the annular and longitudinal drainage blind tube, so that most of the high water pressure from the one-way valve at the elevated arch out of the tunnel. Three-way drainage system pressure reduction ability and its quantity, pipe diameter size and other parameters are directly related, mainly manifested in the greater the quantity, the larger the diameter of the pipe, the more pronounced the effect of pressure reduction. At the same time, the water pressure error between test and theory can be controlled at about 5%. The water pressure variation law of the new three-way drainage pressure reduction system was verified through a combination of experiments and theory. The research results can provide certain reference value for subsequent projects.