Machining of hard steels has it’s own problems. According to the recent advances in implementing of new cutting tools, the machining of hard steels with operations such as turning and milling is possible and it can replaced with some of grinding operations. Turning of workpieces with 45 HRC or upper hardness, is said hard turning. The aim of this article is the investigation of the effect of workpiece hardness and cutting speed and feed rate parameters on surface roughness in hard turning of cold work tool steel X210Cr12 or SPK in dry condition. For achieving this goal, the workpieces of X210Cr12 steel where hardened with different heat treatments cycles such that their hardnesses lie in the hard turning range. Then the workpieces were machined with different cutting parameters using CBN tool and the resulted surface roughness were compared. Experimental tests designed with full factorial method and totally 36 tests have been done. According to obtained results of experimental tests and analysis of variance, the effect of feed rate and workpiece hardness on surface roughness was 90.4% and 8.3%, respectively. The effect of cutting speed on surface roughness is negligible. Increasing the feed rate results in the upper surface roughness. Increasing the workpieces hardness to 50 HRC, decreases surface roughness and increasing workpieces hardness from 50 to 65 HRC, increased surface roughness.