In this paper, the problem of multi-robot coordination for a robot-conveyor system in a pick-and-place task is addressed. To improve the productivity of a robot-conveyor system, the combination of part dispatching rules is utilized to coordinate the action of robots. The greedy randomized adaptive search procedure (GRASP) is utilized to search for the optimal combination of part dispatching rules from a set of candidate part dispatching rules. The proposed method is verified to be effective and practical through a set of tasks in a simulation.