Recently, the hard machining technology has been growing the concern in the metal cutting field. The paper objective is to study the influences of input cutting modes on surface roughness Rq in the hard turning process of DIN 17350 tool steel (60HRC). The interaction effects of cutting speed, feed rate and depth of cut on surface roughness Rq were specified by using Box-Behnken experimental planning design. The obtained findings showed the trend of interaction effects of two input factors while the rest was fixed. From there, the proper value ranges were provided to achieve the smaller surface roughness Rq values. In detail, the cutting speed V=800÷950 rev/min, feed rate f=0.05÷0.07mm/rev, and depth of cut t=0.1÷0.15mm should be chosen to achieve the smaller surface roughness Rq values, which will play the significant meanings in further studies and production practice.