Wireless sensor network (WSN) has many promising applications. One of the most challenging technical issues for sensor network design is to enable ultra low power consumption communication. In this paper we propose a packet compression mechanism, namely EasiPC, as a new power management technique for WSN. With this mechanism, the lengths of data packets are shortened significantly due to the effective reduction of redundant information. As a consequence the energy required for transporting packets is saved too. Experiments carried out on WSN platform developed in-house show that this packet compression mechanism is both feasible and effective. Additional benefits introduced by this packet compression mechanism include reduced transmission delays, reduced channel accessing collisions, as well as enhanced channel utilization.