In order to promote technology of longitudinal-torsional composite ultrasonic vibration processing technology, a longitudinal-torsional composite ultrasonic horn structure is designed to better play its advantages of the hard-brittle materials processing. The mechanism of the vibration transformation of the helical slots is deduced, and the influence of the longitudinal and torsional vibration components on the vibration trajectory of the horn is revealed. A finite element analysis is used to define the torsional and longitudinal component ratio j, analyzing the influence of the parameters such as helical slots number n, helical slots angle θ and slot width d on the torsional and longitudinal component ratio j. j increases with the addition of the number of helical slots n and slots width d, and j increases first and then decreases with the increase of the helical slots angleθ. The primary and secondary influences of helical slots parameters on ratio j are obtained by the difference analysis method of orthogonal parameters. A new method of torsional vibration measurement is developed, and the results of the finite element analysis are verified by experiments.