An efficiency improving device is composed of a round rubber packing ring, a hot water guiding pipe and a cold water guiding pipe, and is characterized in that two symmetrical semi-circular holes are arranged in the round rubber packing ring, the hot water guiding pipe and the cold water guiding pipe are respectively inserted in the two semi-circular holes, and the device is installed in an inner pipe opening end of a vacuum pipe, can effectively overcome the defect of traditional full glass vacuum pipe water heaters in the circulating process, improves the system heat efficiency and the usable heat gain, and lays an excellent foundation for improving the performance of full glass vacuum pipe water heaters.