Field monitoring is one of the main applications of wireless sensor networks, which has the characteristics of long deployment period, battery powered nodes, realtime uploading sensing data and etc. Aiming at the characteristics of this type realtime data acquisition applications, in this paper a scheduling scheme for media access control (MAC) layer based on preamble sequence wake up mechanism is proposed. Through coordinating the scheduling of the node wake up time of the data uploading path, this scheme decreases the length of the preamble sequence of the sender, reduces the node energy consumption and channel contention overhead, and improves the realtime performance of abnormal data uploading. The energy consumption analysis and comparison for multihop tree network between the proposed scheme and the existing lowpower MAC protocols were conducted. The simulation and experiment results verify the effectiveness of the proposed scheme, the proposed scheme greatly increases the network lifetime, while ensures the real time performance and delivery ratio of the data at the same time.