Abstract: The research of task allocation in multi-agent system is becoming more and more. The contract net model is a classical method for task allocation in multi-agent system, but traditional contract net model has lots of deficiencies.With the base of bidding announcement based on the credit of agent and bidding based on self-adaptation, a synthetic evaluation strategy based on the load,capability and credit of bidding agent was also proposed,which can effectively resolve the problem during the procedure evaluating bidding. The simulation experiment proves that the performance ofthe extended contract net is effective.

Key words: Multi-agent system,Mask allocation,Improv}d contract n}t,Synth}tic evaluation