Hydraulic plug for water pressure test is more reliable and flexible than other types of plugs, but difficult drainage and pressure relief after the test have been remained, so its usage is confined to shallow holes or holes with high water levels. This problem was studied and the solution was put forward. New type of hydraulic plug structure was designed for drainage and pressure relief of hydraulic plug, by which the limit of hole depth is broke through and the hydraulic plug can be widely used. The paper introduces this new hydraulic plug about its structure, working principle and engineering application effect.