Abstract: Ant Algorithm is an optimization algorithm that gained by observing the real ant colonies,and it is very useful in solving difficult optimization and distributed control problems.The algorithm is modeled on a concept called “stigmergy” of the ant society.One of the most important problems to the multi robot system is that,when the system is working in an unknown environment,it has to decide which tasks must be done by cooperation of several robots.In this paper,the concept “stigmergy” is introduced to the multi robot system,and a self organization cooperation method enabling different number of robots to cooperate on a task according to the difficulty of it is designed.In addition,the definition of the “Task Deadlock” is given,and an adaptive attenuation factor to eliminate task deadlock is introduced in the cooperation algorithm.Simulation is done to test the algorithm.