Inherent defects insurance is one of the practical tools for building quality management, with the inherent defects risk assessment of buildings as its core. Unfortunately, the domestic Technical Inspection Service has failed to build a comprehensive risk system covering the project. As a result, the risk assessment mainly focuses on the construction process inspection, lacking a risk assessment model with theoretical support for the inherent defects. Therefore, the mechanism of inherent defect risks is analysed in this paper to provide a theoretical basis for the risk assessment. This paper identifies the inherent defects risks and risk factors of buildings and constructs the causal mapping and weights among building quality risks based on the Analytic Hierarchy Process of group decisions using expert interviews and questionnaires. It was found that the risk factors of survey and design, concrete pouring, roof waterproofing, and insulation engineering, and the completion review had a significant impact on the inherent defect risks.