Abstract: Leakage in municipal pipelines is one of the significant contributing factors to urban ground collapse. To investigate the causes of pipeline leakage and the mechanical processes of ground collapse， this study focuses on a ground collapse event in southwestern China. Through field investigations， numerical simulations， and comprehensive analysis of multi-source data， the following conclusions were drawn： the ground collapse was caused by large-scale erosion cavities around pipelines and wells. The primary factors contributing to cavity formation were leakage from sewage wells and adjacent pipe sections， while secondary factors included short-term leakage from stormwater rectangular culverts， stormwater branch pipes， and shallow unidentified water sources. Structural defects，such as those at the bottom of well chambers， around lower well chambers， flow channels， and pipe-well joints，were identified as the root causes of leakage. The ground collapse induced by municipal pipeline leakage went through four developmental stages.It began with pipeline network damage and initial leakage， followed by soil erosion and the formation of interconnected leakage pathways. As the structural defects worsened， leakage intensified， ultimately leading to cavity formation and final subsidence collapse.