Sustainability assessments of marine protected areas (MPAs) are essential for improving the effectiveness of management efforts. Since sustainability is closely related to the concept of intergenerational well-being, measuring and tracking it through time is crucial. Therefore, this study will use the system dynamics approach applied at Pieh marine park as the study site. A system dynamics model was built comprising four sub-models: fish population dynamics, coral reef coverage, tourism, and pollution. The goodness-of-fit test of the model indicated low and unsystematic model error. The sustainability assessment was conducted using the three principles of sustainability proposed by Herman Daly, which define sustainability for resource management based on the change in the amount of renewable resources, non-renewable resources, and pollution. The sustainability assessment determined that Pieh marine park cannot sustain economic activities in its area, indicated by decreasing renewable resource indicators in the form of fish population dynamics, coral reef coverage, and increasing pollution levels. Several management interventions can be applied to improve sustainability, including lowering the total allowable catch, coral transplantation, and improved waste management.