This paper deals with theoretical and experimental investigation into the processing parameters which influence the tapping torque in vibration tapping. Theoretic analysis with fracture mechanics indicates that the pulsating cutting force effect of the tap on the workpiece results in stress increasing, which leads to reduced cutting forces and a much lower tapping torque. And the effect of the increasing stress would decays gradually with increasing cutting distances. Theoretical analyzers have been developed to the relationship between tapping torque and torsional angle amplitude and net cutting time ration in vibration tapping. Large quantity experiments of vibration tapping in different materials with different thread dimension have be introduced. The thread dimension range M3 to M6, and materials of test include C45 steel, 1Cr18Ni9Ti, TC4 and GH4169. Tapping torque wave was measured in vibration tapping. And the experiments were conducted to compare the fluctuation tapping torque with different cutting distance. Experimental results showed that tapping torque would increase with increasing of torsional angle amplitude and net cutting time ration in vibration tapping. And the theoretical results are confirmed by experiments.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.