In this paper, a kind of price-driven load balancing assignment mechanism in wireless sensor network is proposed. A logic price function set for each node, which serves as a reference for the assignment of data traffic when the node is selecting a router. The price-driven situation is analyzed, and the selection criteria of logic price function are given. When the data is forwarded, the node can affect the selection of traffic assigning nodes via regulating the price function according to the data size. Theoretical analysis and simulation results show that the assignment mechanism proposed can effectively control the load balance between the nodes. Moreover, the price strategy of nodes can be changed dynamically, and the traffic assignment of entire network can be affected using this mechanism.