In consideration of the characteristics that loads of nodes and hops to Sink are interrelated in data gathering traffic model,a grade-based unequal clustering algorithm is proposed to solve the load-balancing problem of wireless sensor networks.A traffic-mode-based clusterinig topologic structure is built to realize the load balancing of network and to relieve the traffic congestion around Sink(“Hot Spot” problem). Based on the analysis of the data gathering traffic model,the relationship between the hops to Sink and the load of Cluster Heads(CHs) is given.Then,a grade-based load-balancing clustering algorithm for a wireless sensor network is prensented,in which the cluster size is based on nodes’ grade and the cluster head selection uses mulit-weight.Simulation results show that the standard deviations of CHs’ load with different grades are reduced by 9 times,so that the load balance of the wireless sensor network is improved effectively.