An automatic cutting machine was developed which was used to cut DMC composite materials used in manufacture of manhole cover.When the composite material was in the conveying process, the cutting machine could cut the material longitudinally and transversely, and the shape of the incision should be as smooth as possible.In slitting process,disc cutter was driven by the rotating shaft to realize longitudinal cutting of composite material. In transverse cutting,the slider crank mechanism was used to drive cutter to realize transverse cutting of composite material. By using MATLAB simulation, cutter trajectory of the crosscut mechanism was optimized, the incision line closed to vertical was got.The results show that when the distance between the cutter and the rotating center of the crank/rod is 55 mm and the crank angle speed is 26 r/min,the shape error of the transverse incision of the material is the smallest, and it is most close to the leveling standard, to meet the production requirements.