In order to improve the surface quality of single-crystal silicon by single-point diamond turning in the direction of surface roughness optimization， orthogonal cutting experiment are designed. The effects of spindle speed， feed speed and cutting depth on surface roughness are studied by variance analysis， response surface analysis and range analysis.The results show that the spindle speed has a significant effect on the surface roughness， and the larger the spindle speed is， the smaller the surface roughness value is. The regression model of surface roughness is established.The interaction of spindle speed and feed speed has the greatest influence on the surface roughness by response surface analysis.High-quality single-crystal silicon element with a surface roughness of Ra2.7 nm is obtained with the optimal combination of cutting parameters of 3300 r/min spindle speed，2 mm/min feed rate and 5µm depth of cut.Relatively smooth surface and the banded chip is observed.The material is removed in the ductile state.