The invention provides a new method for detecting an internal defect of a honeycomb, and belongs to the technical field of non-destructive testing. The method combines a transmission method ultrasonicscanning detection technology, a reflection method ultrasonic scanning detection technology and an X-ray detection technology, and individual parts are verified by further assisting by a computer tomography scanning imaging technology. According to the invention, relatively accurate and economical means are adopted to locate, characterize, position and quantify internal defects of parts, so thatthe detection work efficiency and quality guarantee of honeycomb sandwich structure parts are improved, and the smooth completion of a production task is ensured.