Aiming at the problems of low opening efficiency, low positioning accuracy and low opening quality in the large diameter manual opening method of traditional FRP tank, a rotary ultrasonic processing system for the sidewall opening of GFRP tank was designed. The system included the parts of the workpiece transport,clamping, feed drive and tool position adjustment. And the ultrasonic vibration rotary axis and feed system were highlighted. The finite element method was used to design the horn with the hole opener, and the horn structure satisfying the resonant frequency was obtained. The finite element software was used to analyze the harmonic response of the horn with the hole opener. The axial direction is dominant and the vibration amplitude meets the requirements.