The invention discloses a structure and method for treating severe disengagement, cracking and other defects of a tunnel lining. According to the method, original defective secondary lining concrete is chiseled away, and an inverted trapezoidal groove with the inside being wide and the outside being narrow is formed; steel bars are embedded in the middle of the groove in the annular direction and the longitudinal direction, and meanwhile, the steel bars and the original concrete are anchored integrally; self-propelled hollow grouting anchor rods are drilled in the groove area and surrounding the groove at the same time, and the outer side and the inner side, close to the secondary lining, of each anchor rod are wrapped with two water-swelling rubber water stop strips; and after a formwork is erected on the outer surface of the secondary lining, micro-expansion concrete is poured into the groove and is tightly connected with an original primary support and the secondary lining, so that a new lining structure is formed, the outer surface area of the micro-expansion concrete extends around till reaching the design thickness of the secondary lining and then extends again by 80-100 cm within which steel belts are hung for anchorage. The structure and method can effectively treat the defects of severe cracking and disengagement of the lining, the structure stability is good, the mechanical property is high, the problem that the defects occur again in the later period is avoided, the treatment method is high in operability, safe and reliable, and great economic benefits are achieved.