Abstract: For energy management and optimization of wireless sensor network (WSN) nodes, a power state transition model of WSN node is proposed through the analysis of the operation of the main energy consuming components within the node. The model describes the relations and conditions of the transitions of WSN node between different states with different power levels. Since more energy can be reserved when the node is scheduled into the appropriate states with lower power level, a method is introduced to determine the time thresholds for the state transitions. The optimal decision of the time thresholds is based on Markov strategy with certainty. This model can supply a good reference for the design of the dynamic power management of WSN nodes.