The invention discloses a rock joint ultrasonic experimental apparatus under complex stress and a control system thereof; the apparatus comprises a rigid frame, an experimental space is provided in the rigid frame, a horizontal sliding bearing plate is slidably disposed at the bottom of the rigid frame, a dynamometer, an axial ultrasonic vibration transducer, a tangential ultrasonic vibration transducer and an axial loading block are rigidly connected in sequence on the horizontal sliding bearing plate, an axial hydraulic driver is mounted atop of the rigid frame, the piston end of the axial hydraulic driver is in sequential rigid connection to the dynamometer, the axial ultrasonic vibration transducer, the tangential ultrasonic vibration transducer and the axial loading block, four tangential hydraulic drivers are horizontally mounted at the front, back, front and left of the rigid frame respectively, the piston ends of the tangential hydraulic drivers are each connected to a tangential loading piston, and the other ends of the tangential loading pistons are in sequential rigid connection to the dynamometer and the tangential loading block. The rock joint ultrasonic experimental apparatus under complex stress and the control system thereof allow stress field state of a joint face in underground rock to be simulated for ultrasonic dynamic experiment.