Surface roughness is an effective factor in determining the fatigue life of machine elements. Roughness of the surface results in the notch effect, and if the notch effect increases, the fatigue life of the material is shortened. 20 mm thick steel AISI 1050 (CK45, DIN 1.0540, EN C50) was cut into 80x80 mm squares by applying the abrasive water jet machining technique. The square cutting operations were carried out at five different feed rates (10, 16, 24, 34 and 45 mm/min) and the other cutting parameters were kept constant. The Rz and Sm surface roughness values of the four surfaces obtained at each feed rate were measured. The effect of the feed rates on the surface roughness was investigated. Also, by applying the Murakami surface roughness fatigue model, the effects on the theoretical fatigue life of the surface roughness resulting from the chosen feed rates were modelled. Furthermore, the reason for the difference in surface roughness values between the first, the second, the third and the fourth surface at each feed rate was investigated. As a result, an increase in the feed rate causes an increase in surface roughness values, which in turn shortens the fatigue life of the material. The surface roughness value measured on the first surface of the four cutting surfaces obtained at the same feed rate increases on each surface and reaches the highest value on the fourth surface.