Information systems acceptance has long been an interesting topic for both researchers and managers. It is necessary to understand user’s attitudes and behaviors toward an information system so as to evaluate the consequence of system implementation. Different from previous research, this study investigates user acceptance toward a newly introduced system from a behavioural economics perspective. Specifically, the study targets the effects of system usage outcomes on user satisfaction in a mandatory context where an old system is replaced by a new one. Based on the Prospect Theory, we argue that users evaluate the new system according to their perceptions from a value function, comparing their current system usage status with a reference point in terms of gain and loss. By describing a three-stage system switching process, this study unpacks how the usage outcomes of both the old and the new system and their contrasts affect perceived value toward the new system, which positively predicts user satisfaction. The system usage performances related to both the old and the new system are incorporated in the research model. Their joint effects, the main and the interacting effects, on user satisfaction with the new system are explicitly explored and explained. Findings of the study enable firms to better understand a system switching process and to design more effective managerial interventions for improving new system acceptance.