Optimum path planning for multi-robot H-beam cutting system is presented to improve work efficiency. According to the working and design features of the multiple robots system, the minimum time delay method is adopted to avoid collision, and collision avoidance and path planning can be abstracted to a mathematical model to be optimized. Fast collision detection for the system is put forward based on analyzing the mode of collision. The concepts of collision map and interference zones are introduced and mathematic model of optimum path planning is constructed based on interference zones to compute the minimum delay time. We use the off line programming to compute the delay time and build database of optimum paths for all of cutting types. From the simulation result of a cutting type of H-beam, we can achieve the goal of improving work efficiency through the optimized path.