Background: Situated simulation is a pedagogical method used for on-the-job training in many occupations. Establishing a framework that uses mobile devices to provide both simulation elements and incorporates instant feedback as reasoning scaffolding is a promising and relatively unexplored research topic. Objective: In this study, we designed a simulation game framework with mobile instant feedback to help learners develop high-risk emergency decision-making skills. According to the learners' different emergency decision-making, the mobile game provides instant feedback on the subsequent development of different medical conditions and provides the guidance of an instant reasoning scaffolding to help learners immediate correction strategies. In this study, we analysed the learners' learning effectiveness and psychological responses to the instant reasoning scaffolding-based game-based training, including flow, motivation and activity anxiety, as well as analysing the fidelity of the game. Methods: A quasi-experimental design study with a total of 96 volunteers participated was grouped into Experimental group 1 (game with instant reasoning scaffolding), Experimental group 2 (game with document scaffolding) and a Control group (general case study with document scaffolding). Results and Conclusion: The results showed that participants who participated in instant reasoning scaffolding-based game-based training had better learning effectiveness than those who participated in document scaffolding game training and general case study. Participants in the instant reasoning scaffolding-based game-based training were able to achieve high flow, high motivation and low anxiety, and this scaffolding-based game framework has the potential to be extended to various emergency decision-making training areas.