Surface roughness is an important parameter determining the quality of machine elements, with the desire to reduce surface roughness to increase the quality of the product. This paper uses the experimental design method of Taguchi in combination with genetic algorithm (GAs) to study the optimization of surface roughness of machine elements when external cylindrical grinding 9CrSi steel. The smallest surface roughness achieved is Ra = 0.258261 m when feed rate Sd = 0.3 m/min, the rotation speed of the workpiece nw = 100 rpm, and the depth of cut t = 0.005 mm