A pipe connecting structure including a male flange block combined with a first pipe and a female flange block combined with a second pipe, which is fastened to the male flange block by a fastener, where a protrusion having a hole that communicates with the first pipe is formed through the male flange block, and an insert portion into which the protrusion is inserted is formed through the female flange block, and a sealing member to closely contact with the end face of the protrusion is seated on the bottom inside the insert portion, and the sealing member includes an inner sealing part of soft metal and an outer sealing part of rubber tightly fitted around the outer circumference of the inner sealing part. Therefore joints between pipes, a heat exchanger and a pipe, or two components can bear high pressures in a refrigerating cycle system using a CO2 refrigerant, air tightness can be maintained under low and high temperatures without changes in quality and shape of a sealing members, and it is possible to prevent and minimize leakage of the refrigerant by preventing permeation of CO2.