In this paper, we propose a context-aware reminding system to assist dementia elders for their daily activities. We particularly focus on the issue of conflict detecting and handling in the real-world reminding applications. We adopt a planning approach to describe the constraints of reminders, and transform the constraints into temporal constraint graph for reminder conflict detecting. In real-time reminder scheduling, we define three disruptive activities, and present a context-aware reminding strategy to handle the conflicts between pre-planned and disruptive activities. Finally, the system prototype is introduced.