This paper introduces a deep sea pressure - tight rock core smpling technology with hydraulic transport of rock core from the drilling tool to the pressure - tight core barrel. When rock core is drilled and released from the drilling tool,the naked free core is then hydraulically transported from the inner core tube to the on - the - rack pressure - tight core barrel,and when the core in the pressure - tight core barrel is recovered from the sea bottom,it is possible to connect the pressure - tight core barrel to the pressure - tight experimental equipment in the lab, and shift the core into the pressure - tight experimental equipment in pressure - tight condition. The paper provides the theoretical analysis and the experimental data of the hydraulic transport of the core,and briefly introduces the formation and working principle of a practical deep sea pressure - tight rock core sampler designed with this new technology.