Abstract: To enable the non-destructive evaluation of quality uniformity in closing resistor plates prior to their installation in UHV equipment, this study optimized the detection process for crack defects using ultrasonic hydro immersion scanning technology. The influence of key detection parameters was systematically investigated. An integrated system evaluation method is proposed, which incorporates detection probability, noise level, a refined signal-to-noise ratio metric, and scanning time. This method was used to analyze the effects of detection frequency, scanning step interval, focal position, and imaging method on the inspection results. The detection process was optimized and its effectiveness was validated. The results indicate that the optimal detection performance was achieved with the parameter combinations: “5P6F25-0.62 mm-upper focus-bottom wave imaging” and “2.25P6F10-0.62 mm-middle upper focus-bottom wave imaging.” The ultrasonic waves with a detection frequency lower than 5 MHz have strong penetration. When combined with bottom-wave imaging, the detection effect is the best, with a defect detection rate of 100%. The refined signal-to-noise ratio (SNR) metric was significantly better than that obtained with high-frequency probes. At frequencies exceeding 7.5 MHz, severe ultrasonic attenuation led to a complete loss of the bottom wave signal and a detection probability of 0. A scanning step interval of 0.62 mm reduced the total scanning time by 40% compared to 0.31 mm interval, while maintaining the same detection probability. 3D C-Scan imaging results confirmed the reliability of the optimized process for detecting both surface and sub-surface cracks in the resistor plates.