Collision between limbs of multi-robot systems is studied in this paper. Combining mechanism principles with geometric analysis, we obtain interference surfaces, zones and evasion direction expressed bylimb dimensions and distance between robots. Very litt1e computation is needed to determine the surfaces,zones and directions. Several typical surfaces and zones are analyzed in detail, formulations expressing thesurfaces, zones and directions of various two-robot systems are given and collision avoidance strategies of multi-robot systems are discussed. The study reduces greatly the computational burden and explore a newway for intelligence control of multi-robot systems at joint level.