This study identifies the pattern of software defects for each system company based on the defect DB in the operation and maintenance stage built by DTaQ, and derives factors to support customized quality management. Through the analysis of the cause of software engineering change in the land weapon system sector conducted in 2021, it is expected that defects that may occur in the future can be identified at an early stage as the quality control elements suitable for the characteristics of each system maker are returned to the development stage.