The communication efficiency of large-scale WSNs with high node density is highly related with specific forwarding strategy in complicated wireless environments. Thus, it is the key problem that how to use the characteristic of high-density to select appropriate forwarding nodes to relieve the load imbalance and improve the communication efficiency. In this paper, we first propose a Fine-grain Gradient Sinking (FGS) model and several data forwarding strategies based on this model. Then we give the criteria of communication efficiency and emphatically analyze the communication efficiency of various forwarding strategies. Simulation results show that forwarding strategies under FGS model can achieve higher communication efficiency, and the efficiency can be further elevated by introducing the statistics of packet receive rate during the forwarding process.