Effect of cutting conditions on cutting forces was investigated when turning 42CrMo steel using coated cemented carbide cutting tools. The influence regularity of cutting force was obtained when cutting parameters were changed. The changing cause of cutting forces between different cutting conditions was analyzed comparatively, considerable cutting conditions were provided. The experimental results indicate that cutting depth and feed rate have larger effects on cutting forces, while the effect of cutting speed is less. The effect of the cutting depth on the feeding force is more than back force, and the feed rate exerts more influence over back force. The change of total force is similar to cutting force.