Wireless sensor networks (WSNs) significantly plays an important role in the Internet of Things. Thus it is vital to design a good power saving protocol, which operates at the medium access control (MAC) layer, for a WSN since sensors are generally battery-powered. Wireless sensor network is organized as a corona for achieving low-overhead routing. In this project, we propose an optimal and maximized configurable power saving protocol, named Green-MAC, for a corona-based WSN, which has some specific features. The features are generalized Chinese remainder theorem which guarantees that any two sensors in the neighboring coronas can simultaneously wake up, the cycle length and pattern which is considered with the ATF-ratio (i.e. the fraction of awake time frames in a cycle) of each sensor, the number of configurable ATF-ratios which is proposed for Green-MAC such that the power consumption of a WSN can be minimized while the worst event-to-sink delay requirement can be fulfilled with high probability. The simulation results outperforms the existing power saving protocol for corona-based wireless sensor networks. The results is obtained in the analysis of the performance of the simulation.