Based on the orthogonal experiment,Al2O3-TiCN carbide alloy coated tools were used for dry cutting of N-type HT250 gray cast iron.The effect and mechanism of cutting speed,feed rate and back engagement of cutting edge on surface roughness were studied to provide a theoretical basis for N-type HT250 cutting.The results show that the surface roughness of cutting N-type HT250 using Al2O3-TiCN carbide coated alloy tool is better than that of ordinary HT250.Especially in the case of low cutting speed(vc=100 m/min),N-type HT250 surface roughness is more excellent.The most significant factor affecting the surface roughness of N-type HT250 is the feed rate,followed by back engagement of cutting edge,and the influence of cutting speed is relatively small.The surface roughness increases with the increase of feed rate,and decreases first and then increases with the increase of back engagement of cutting edge.When ap=1 mm,the comprehensive performance of the surface roughness is the best.