In open environments such as the Internet agents from heterogeneous sources could exist and interact to accomplish joint activities.The general Contract Net Protocol model which works on bids invitation between a Manager agent and Contractor agents can successfully realize the cooperation among agents.But it also faces many problems such as the high network traffic and low adaptation to the changes of the contractors' capacity and load.So in this paper

the concepts of grade field and timing consumption are put forward and introduced into the general contract net protocol and a new model of grade field and timing consumption contract net model is made.By dividing three different grades subfields according to the capability and success rate in all the service agents

the intercooperation of the service agents is limited in grade field 1.The theoritic analysis and the experiments show that this new model can reduce the searching range and lighten the network.traffic.Furthermore it can balance the load of the contractors.