Abstract: The brazed rate of micro-honeycomb brazed composites is an important basis for optimizing the brazing process, quality inspection and product acceptance, and its non-destructive testing methods have always been a research hotspot in related fields. In this paper, a hexagonal honeycomb ring (with a single honeycomb diameter of 0.55 mm) that was brazed on the inner surface of high-temperature alloy ring with diameter of 300 mm and thickness of 20 mm was seclected as the research object. Through optimizing the parameters of ultrasonic C-scan probe, such as frequency, focal length, step size and focus size, the feasibility of quantitatively characterizing the brazed rate of micro-honeycomb brazed composites was explored by water-immersion ultrasonic C-scan technology. Based on the experience of frequency gradient design and parameter matching optimization, three types of probes with frequencies of 10, 20 and 30 MHz were selected respectively, and the corresponding focal lengths, step sizes and focus sizes were matched for experiments. The results showed that a relatively clear honeycomb image could be obtained with probe frequency of 30 MHz, the focal length of 31.75 mm, the focus size of 0.16 mm, and the step size of 0.05 mm, and the minimum resolution feature size reached 0.05 mm. The images were proportionally enlarged, and the diameters of these structures were measured to be 0.56 mm, which was consistent with the actual micro-honeycomb diameter of 0.55 mm. Combined with the definition of brazed rate (the ratio of the actual effective metallurgical bonding brazing seam area of the brazed joint to the total brazed area designed), water-immersion ultrasonic C-scan technology was adopted to calculate quantitatively the brazed rate by obtaining the ratio of the clear honeycomb image area to the total scanning area of the workpiece.