For patient safety, this study aims to evaluate the effectiveness of additional objective structured clinical examination (OSCE)-based medical simulation courses to establish the "emergency-stabilization" subcompetency of postgraduate first year (PGY-1) residents.In the simulation course, trainees were randomly divided into three groups: intervention, regular, and control group as Trios-OSCE trainees, Single-OSCE trainees, or OSCE observers (feedback-givers) after attending the pre-OSCE common simulation workshop. Three PGY-1 residents rotated through the Trios OSCE long-station together, while single PGY-1 residents rotated through regular OSCE alone and the control group gave feedback after observation of their peers' OSCE performance. Using Queen's simulation assessment tool, either in Trios-OSCE or Single-OSCE, performance levels were rated as either inferior, novice, competent, advanced or superior in the "therapeutic actions" and "communication" domains. The "overall performances" of all trainees were graded by qualified assessors, experienced facilitators, and standardized senior nurse.The proportion of "overall performance" of trainee's, rated by an experienced facilitator as "above competent level," was significantly higher in intervention group A than in regular group B. After training, the degree of increase in self-efficacy scores was higher among the intervention group than the regular and control groups. In the follow-up stage, a trend of increasing self-efficacy scores was noted in both the interventional and regular groups. For all trainees among the three groups, high postcourse value scores confirm that the new Trios-OSCE model meets the needs of trainees and also motivates the self-directed learning and self-reflection of trainees.Our results provide initial evidence that the new emergency-stabilization-enhanced Trios-OSCE-based medical simulation course including the additional training capacity offered by adding an observer group had positive effects on PGY-1 residents' self-efficacy and clinical transfer.