WSN (Wireless Sensor Network) is constrained by limited radio propagation range as well as battery life. Multicast is an efficient method to support group communication and decrease communicating energy. It is challenging to design multicast routing protocol for WSN. The mesh-based protocol ODMRP (On-Demand Multicast Routing Protocol) is our focus. Its forwarding group can be used not only for delivering multicast traffic from base station to sensor nodes but also for reverse routing from sensor nodes to the base station to assemble data. The feasibility and improvement of ODMRP for WSN are analyzed by modeling and simulation. Results show that associated with network design including node density and initial energy we can apply ODMRP efficiently.