Mobile agents (MA) have been widely applied in detecting abnormal events in wireless sensor networks. Based on the characteristics of the event, the data center (i.e., the sink) sends a specific MA to collect the data sensed by the sensors (acted as source sensors) in the nearby area of the target event. Different from the traditional client-server transmission model, the MA technology can compress and aggregate the sensed data and reduce the amount of data and the energy consumption of sensors for data transmission. When MA passes more source sensors, the size of the collected data becomes larger. This paper investigates the existing MA itinerary planning algorithms, and proposes an agent data separation strategy. The strategy can determine whether to send the collected data to the sink in advance based on a data separation rule. If data separation is performed, the data collected by the MA will be sent to the sink, while the MA only with the head will continue visiting the rest source sensors. Because the data carried by the MA is reduced, the proposed agent data separation strategy conserves the energy consumption of sources sensors. The strategy is a general scheme and can be applied in most of the existing MA itinerary planning algorithms to enhance their performance. The ultimate goal of the proposed strategy is to reduce the data transmitted by source sensors and extend their working lifetime for monitoring the targets.