We design a "two-layered" dynamic power management strategy in our sensor node to reduce the power consumption. There are many factors such as the probability of event generation, the battery status, the coverage problem, and the communication situations in our consideration. In network communication, we propose an asynchronous awakening scheme so that each node is free to power on or off its components based on the observed event statistics, and make a trade-off between communication and power consumption. The deepest sleep state period is determined by taking account of the residual power. Combining with these methods, the lifetime of the sensor node can be extended as longer as possible without influencing the system performance.