Taking the "closed-door" tunnel collapse with high safety risk as the research object, based on the innovative technical route of "three-section and four-step" method, it is verified by engineering example and the summary is carried out. On the basis of successfully treatment of many such large tunnel collapses, the relatively common "three-section and four-step method" safety treatment technology for treatment tunnel collapse treatment is innovated ("three-section" refers to the collapsed section and the collapse-affected sections at both ends, "four-step" refers to the steps of sequential construction). This technical method takes the tunnel collapse section, the visible collapse affected section immediately adjacent to the tunnel collapse section, and the invisible collapse affected section as the treatment objects. The main technical method of "three-section and four-step" method is: after the tunnel collapse, first, according to the actual engineering geological condition of collapse section and the collapse affected section, collapse condition, collapse cavity stability, deformation, design and construction of the collapse affected section, to comprehensively analyze and judge the safety risk of each section, and evaluate the safety risk in sections. Second, according to the result of safety risk evaluation, to determine the reasonable construction sequence and steps according to the way of gradually advancing from the position with low safety risk to the position with high safety risk. According to this technical method and the corresponding technical scheme, the treatment of the "close-door" tunnel collapse is completed. Taking the "close-door" tunnel collapse of Wangmazi tunnel No. 1 emergency parking zone for example, through scheme comparison and selection, the tunnel collapse is treated safely and effectively treated by using the "three-section and four-step" treatment technical method and the corresponding technical scheme. Practice has proved that the "three-section and four-step method" is a safe and effective technical method to treat the "closed-door" tunnel collapse, it has versatility, operability and safety.