Abstract: The present invention relates to a method for repairing and reinforcing an underground pipe. The method of the present invention comprises the steps of inserting an inner mold made of flexible material through the interior of a reinforcing element including a fiber preform surrounded by impermeable inner and outer tubes made of the flexible material and combining the inner mold with the reinforcing element; positioning a combined element, which includes the reinforcing element and the inner mold, into the underground pipe to be repaired and reinforced; injecting and expanding the inner mold with and by high temperature fluid, and brining the reinforcing element into close contact with an inner wall of the underground pipe; injecting the reinforcing element with thermosetting resin; and removing the inner mold after the thermosetting resin has been cured.