Objective To explore the influence mechanisms of assurance factors within Jiangsu Province′s Standardized residency training (SRT) on training quality, and to inform future optimization of the management framework of Standardized residency training. Methods A questionnaire-based study was conducted from April to June 2024. Using stratified random cluster sampling, 543 residents from 13 prefecture-level cities in Jiangsu Province were selected to assess the current status of SRT assurance factors and training quality. Factor analysis was conducted to identify critical components of the assurance factors, followed by structural equation modeling (SEM) to analyze their impact pathways on training quality. Bootstrap testing was applied to examine the mediating role of residents′ learning engagement between safeguarding factors and training outcomes. Results Exploratory factor analysis (EFA) revealed three core safeguarding dimensions: structural safeguards, process safeguards, and pedagogical safeguards. SEM demonstrated that structural assurance (β=0.340), process assurance (β=0.155), and teaching assurance (β=0.261) all have significant positive effects on training quality (all P<0.05). Mediation analysis showed: Partial mediation by learning engagement for structural safeguards (indirect effect: 48.3%); Full mediation for process safeguards (indirect effect: 84.7%); No mediation observed for pedagogical safeguards. Conclusions Optimizing residency training requires prioritized structural assurance (such as resource allocation), refined process management (such as salary and benefits), enhanced teaching quality (such as teacher training), and activation of learning engagement mechanisms, offering evidence-based policy pathways for sustainable quality improvement.