The power management system design is a key factor to determine the stability of a sensor nodesbased network environment. In the meanwhile, an application-based resource reconfigurable operating system can enhance the availability, maintainability and flexibility to the required services. In this paper, we propose an integrated power-saving mechanism and reconfigurable approach for the OS design consideration and demonstrate the critical application in farm monitoring and ubiquitous healthcare. To support fast mobile OS porting and implementation, we also propose the on-line retrieval-on-demand design concepts to carry out highly flexible system architecture. Its corresponding applicability in sensor network environment is discussed. The system design cost is evaluated and several simulations for different parameters are conducted and verified.