Abstract: This paper intriduces a pulse echo ultrasonic C scan imaging technology based on multi-electron gate aiming to test variable thickness laminates structures which are extensively used in composite parts. The basic principle is to set a plurality of end to end gates on the echo of surface and bottom for the thickest area of variable thickness laminate to collect the signal and form several pairs of C scan images, which can obtain the internal defects information of different regions by analyzing these images. This technology can solve the problem of bottom wave shifting in pulse echo method. The feasibility of this technology is well proved by using ultrasonic C to detect the variable thickness laminates with artificial defects.