Abstract: A CFRP drilling testing platform was set up to discuss step drill structural parameters and drilling process parameters under composite drilling axial force and delamination factor influence based on the VMC850B vertical machining centers and UltraPAC ultrasonic C-scan. The result shows that drill process parameters have significant influence on the first section of the drilling thrust and step drill structural parameters have significant influence on the second section of the drilling thrust. The value of delamination factor is connection with the first section of the drilling thrust and the second section of the drilling thrust. When d/D >0.5, the size of delamination factor is mainly connection with the first section of the drilling thrust. When the first paragraph diameter and the second point angle are 2.8 mm and 95°, spindle speed and feed speed are 7000 r/min and 2.5 mm/s, the delamination can be reduced.