In Wireless Sensor Network, data fusion or data aggregation is the key technology to decreased power consumption and improved accuracy of data collection. This paper proposes a new data fusion approach which is based on the mobile agent technology. It uses mobile agent communication to decide the filtering or merging of data. It also makes use of XML as the expressive mechanism for sensed data, network topology, and agent’s inner framework. An experiment is designed to evaluate the proposed approach with the existing data fusion technology. It is found that the new approach exhibits better performance in data fusion efficiency and power consumption savings.