During the backfilling process of the basement floor of a high-rise residential building,one of the frame columns under the basement was crushed,and adjacent beam members showed signs of cracking. In order to investigate the cause of the accident,on-site investigation,concrete strength testing,core sampling,and ultrasonic testing for poor compaction were conducted. Based on the actual load-bearing conditions of the structure on site,the bearing capacity of the crushed column under different conditions was calculated. The analysis showed that the main cause of the accident was the serious segregation defect in the concrete of the frame column,while the secondary cause was overloading of the topsoil during backfilling and the impact of the excavator during construction. This paper can provide some preventive lessons for similar engineering accidents in the future.