Abstract: This article systematically analyzes the causes and damage mechanisms of a local floating and cracking accident (with a maximum floating value of about 170 mm) that occurred in the basement floor of a large commercial square in Guangzhou through on-site investigation and theoretical exploration. The investigation and analysis results indicate that the failure to timely backfill the soil cover in the basement roof design resulted in insufficient structural weight, coupled with quality defects in the early construction of the floor, which collectively induced the basement floor to float and crack. Although the subsequent use of anti floating anchor cables effectively controlled the overall arching, the on-site grouting measures used to deal with the cracking and leakage of the bottom plate increased the additional instantaneous pressure on the bottom plate, resulting in the failure of the anchor head near the grouting hole, which led to the second local cracking, leakage, and arching of the bottom plate. To solve the above problems, this article proposes a comprehensive treatment plan based on the latest basement conditions, which combines anti drainage and system governance. Firstly, emergency measures for water release and pressure reduction are taken to quickly stabilize the structure. Considering the possibility of leakage from the rear anchor cable, a triple treatment measure is integrated, which includes a composite plate (reinforced counterweight), a drainage plate (active drainage of leaking groundwater), and an anti floating anchor cable (providing long-lasting anti pull force). This comprehensive management method effectively controlled the floating of the basement and successfully restored the normal use function of the underground space. It is hoped that it can provide reference and inspiration for similar basement anti floating problems.