In order to study the influence mechanism of polyurethane grinding rod on the surface grinding quality of alloy gray cast iron, polyurethane grinding rod was selfmade, and diamond abrasives with particle size of 1, 6 and 9 μm were added to the grinding rod to grind alloy gray cast iron respectively. The surface morphology and average surface roughness (Ra) of alloy gray cast iron after grinding were analyzed and compared by optical microscope and white light interferometer. The results show that when diamond abrasive with particle size of 9 μm is used to grind the surface of the workpiece, the grinding trace is deep and the surface roughness is poor; in contrast, the optimum surface roughness can be obtained by grinding workpiece with diamond abrasive with particle size of 6 μm, and the Ra value can be reached 0.01 μm; while the grinding ability of diamond abrasive with particle size of 1 μm is very poor, the actual surface roughness is not ideal when the material is pushed to both sides of the abrasive.