In many social insect societies, the repeated action of the insects interacts over time with the changing physical environment to produce a collective intelligence and accomplish task cooperatively. The major mediating factor in this phenomenon is stigmergy, the individual's behavior is induced by sensing the local environmental changes produced by previous behaviors. Inspired by this biological phenomenon, the multi-robot system for collective clustering task consists of homogenous robots with only local sensing ability and four simple reactive behaviors. There don't need any centralized control, global planning, or explicit communication between the interacting robots. The robot's behavior is only induced by sensing the local environmental changes. The simulations show that robots can group a class of objects within a continuous area. Additionally, different conditions are considered and discussed comparing their performance and efficiency