The MAC (medium access contro1) protocol of traditional wireless sensor network has a problem with the high energy consumption of nodes. This paper proposes a CLEE-MAC (cross layer based energy-efficient MAC) protocol using the thought of cross-layer design, based on adaptive S-MAC (sensor MAC) protocol. The CLEEMAC protocol changes the format of control packets of S-MAC protocol with the information coming from a routing layer. It makes the most and reduces the overhearing listening, and at the same time, simplifies the control overhead of multi-hop transmission, improves the utilization of nodes energy, and reduces the delay of data transmission.