Abstract: This study investigated the gate adjustment of ultrasonic A-scan signals in the process of ultrasonic C-scan detection system, and proposed a multi-gate dynamic tracking method suitable for workpieces with variable thickness. The basic principle was to set the detection gate on the echoes between the surface and bottom of the variable thickness workpiece, and the detection gate simultaneously tracked the surface echo and the bottom echo. This method can improve the circumstance when the surface or the bottom of the variable thickness workpiece changed during the detection process, it reduced the influence of interference waves and maximized the effective data collected by the gate. Finally, the feasibility of the multi-gate dynamic tracking method was verified by using water immersion ultrasonic testing to detect variable thickness stainless steel plates with artificial defects.