The purpose of this is to analyze experimentally how the change of cutting speed have effects on hole over size of cutting hole, surface roughness of workpiece and roundness during the deep hole machining of SM55C with solid BTA drill using BTA drilling system. Conclusion reached is as follows. (1) The diameter was expanded for 25$mu$m at the first section and then was reduced 0$mu$m and 15$mu$m respectively at the 10m and 20m section comparing to the diameter of tool with respect to the variation of cutting length at 70m/min of cutting speed. 0.15mm/rev of feed. (2) It was proved that roughness was below 8.67$mu$m for the whole section of cutting length. (3) The roundness has been below 12$mu$m. Regarding the polygon phenomenon, it has been proved that not only uneven best at 70m/min of cutting speed. 0.15mm/rev of feed.