This paper presents algorithms for role assignment and formation control in multi-robot systems. Two circumstances have been discussed. One is with fixed target formation positions, and the other is without fixed target formation positions. For the former circumstance, a modified Hungarian algorithm has been proposed to assign a role for each robot with the purpose of consuming less time to form the target configuration. For the latter circumstance, the appropriate target formation location has been determined firstly. The algorithm based on both total distance and consuming time has been proposed. In the end, the desired configuration has been formed based on the distance-angle method with a virtual leader. Simulation results are presented to validate the proposed algorithms.