Abstract: Cutting is the key to dring speed in tunnel drilling and blasting.In order to study the relationship between the ultra-depth of cutting hole and the utilization rate of hole in the tunneling process of metal mine，the reasonable value range of the ultra-depth of cutting hole and other holes was discussed based on some relevant literature since 1990s and field test results of the ultra-depth cutting hole.The study results show that whether in metal mines or non-metal mines， with the continuous expansion of tunneling engineering quantity，the depth of hole gradually increases，but the ultra-depth of cut hole does not change.According to the statistics of the ultra-deep cutting of some metal mines，95.2% of the metal mines' roadway blasting and excavation under 200 mm. Based on the field test results of cutting hole ultra-deep，under the premise of keeping other parameters unchanged，the ultra-deep length of the cutting hole is used as a single variable，it is concluded that the auxiliary hole and the surrounding hole are 1.8 m and 2.0 m respectively，and the optimal ultra-deep corresponding to cutting hole is 300 mm and 400 mm respectively， which gets the extreme value of hole utilization 97% and 95%， and increased by 5.4% and 10% when compared to the ultra-deep length of 200 mm，the variety of the ultra-deep length of the cutting holes has an important influence on the utilization rate of the holes.Aming at the optimization problem of overdepth length of cutting hole，the concept of overdepth coefficient [η] is introduced，when the depth of the auxiliary hole and the surrounding hole is x， the corresponding hole depth of the cutting hole is y，and there is an optimal cutting hole ultra-deep coefficient [η]，which makes the utilization rate of the blasthole highest.

Key words: Metal mine, Drilling and blasting method, Straight wedge composite cut, Roadway driving, Depth coefficient