Taking the “closed-door” tunnel collapse with high safety risk as the research object and based on the innovative technical route of the “three-section and four-step” method, the summary was carried out and verified by engineering example. Based on the successfully treatment of many such large tunnel collapses, the relatively common three-section and four-step method safety treatment technology for tunnel collapse treatment was innovated (“three-section” refers to the collapsed section and the collapse-affected sections at both ends and “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 the three-section and four-step method is as follows: first, after the tunnel collapse, according to the actual engineering geological condition of collapsed section and the collapse-affected section, the collapse condition, the collapse cavity stability, deformation, and the design and construction of the collapse-affected section are comprehensively analyzed, the safety risk of each section is judged, and the safety risk in sections is evaluated. Second, according to the results of the safety risk evaluation, the reasonable construction sequence, and steps according to the gradually advancing from the position with low safety risk to the position with high safety risk is determined. According to this technical method and the corresponding technical scheme, the treatment of the “closed-door” tunnel collapse is completed. Taking the “closed-door” tunnel collapse of Wangmazi tunnel Number 1 emergency parking zone as an example, through scheme comparison and selection, the tunnel collapse was treated safely and effectively using the three-section and four-step treatment technical method and the corresponding technical scheme. Practice has proven that the three-section and four-step method is a safe and effective technical method to treat the “closed-door” tunnel collapse, and it has versatility, operability, and safety.