The quality of the water-flowing structures buried under the road plays a decisive role in the safety and reliability of the whole project, especially in the collapsible loess area. The leakage protection design of underground concealed engineering is one of the important contents of engineering design. The drainage box culvert is arranged along the length of the road under Fangta Avenue in Yan'an. A landslide adjacent to the road has caused the damage of partial road section of box culvert. Combined with the reinforcement design of the damaged section of the box culvert, the design scheme for the water stop failure at expansion joint, crack at expansion joint, micro-crack at culvert body and concrete surface falling off of culvert body are summarized, and the treatment steps and matters needing attention are set forth in detail. After more than one year of operation monitoring, its engineering quality is good, and it has withstood the test of a rainy season, which can provide the reference for the similar projects in the future.