As Wireless Sensor Network (WSN) has been widely accepted, the network is expected to be applied to environmental measure in yards and gardens. Because stable electric power supply is not available in environmental measure, WSN is generally powered by battery. Improving energy efficiency is important in order to extend operation time of WSN. On the other hand, in actual environmental measure, values of sensors do not vary significantly, and neighbor sensors indicate similar values in stable condition. This research proposes Group Control Method as a new power-saving technique. This Method utilizes the similarity of the values among neighbor sensors and time-stable sensor value in environmental measure. The method forms sensor groups and adjusts sleep time of the network nodes to reduce power consumption. This paper shows effectiveness of power consumption and sensing accuracy based on simulation evaluation.