Abstract: Aluminum alloy bars are the primary raw material for aerospace forgings, and nondestructive testing (NDT) techniques can effectively prevent defective billets from entering the forging and finishing processes. Large-diameter bars face challenges in terms of insufficient detection sensitivity due to the large detection depth, wide detection range, and curved detection surface, making small defects prone to being missed. Therefore, ultrasonic layered focusing detection technology was employed to achieve high-precision inspection of large-diameter bar materials. An automated detection system for layered focusing of bar stock was developed, and test blocks was designed and fabricated for calibration purposes. A dedicated sensors and a layered focusing scheme were designed, and a signal processing method was proposed to improve the signal-to-noise ratio (SNR) and enhance the quality of the detection images. Experimental methods were used to validate the detection capability of the ultrasonic layered focusing technique. The experimental results showed that, using the focused-zone layered focusing detection method, the detection sensitivity within the depth range of 0~60 mm could reach the equivalent of a ϕ0.3 mm flat-bottom hole. The application of the improved soft-threshold wavelet decomposition technique led to an SNR improvement of over 67.08%, significantly enhancing the quality of the detection images.