This paper presents a system-level power management technique for energy savings of event-driven application. We present a new predictive system-shutdown method to exploit sleep mode operations for energy saving. We use an exponential-average approach to predict the upcoming idle period. We introduce two mechanisms, prediction-miss correction and prewake-up, to improve the hit ratio and to reduce the delay overhead. Experiments on four different event-driven applications show that our proposed method achieves high hit ratios in a wide range of delay overheads, which results in a high degree of energy with low delay penaties.