In a resource constrained wireless sensor network (WSN), communication tasks can be expensive in terms of power consumption. Thus, when good communication is required, a mechanism that can maximize the chances of a successful transmission of information via wireless network is very desirable. The Opportunistic Routing (OR) protocol [1, 2] has been proposed as an alternative and efficient method for exploiting the spatial and temporal characteristics of a wireless network. In this paper, we propose an analytical framework model based on Markov Chain of OR and M/D/l/K queue to measure its performance in term of end-to-end delay and reliability in wireless sensor network. The performance predicted by the proposed framework is validated through simulation and is in very good agreement. We also discuss the enhancement strategy on OR to achieve better QoS guarantee in term of delay constraint.