Aiming at the challenge of efficiently and accurately evaluating the stress state of plate components in fields such as aerospace and energy equipment during processing and service, a high-precision ultrasonic stress detection and 3D visualization analysis system based on critically refracted longitudinal (Lcr) waves has been developed. This system is designed to provide a non-destructive, rapid, and quantitative technical means for assessing the stress state of components. Based on the acoustoelastic effect of Lcr waves, a quantitative relationship model between stress and the difference in ultrasonic wave propagation time was established. The system adopts a hardware-software co-design architecture: the hardware integrates a high-voltage spike pulse excitation circuit with a peak voltage of 300 V, an AD module with a maximum sampling frequency of 500 MS/s, and an ultrasonic probe and wedge combination that meets the first critical angle incidence condition. The software optimizes waveform data using wavelet hybrid threshold denoising technology, combines the cross-correlation method to calculate the acoustic time difference, and achieves accurate stress resolution while also providing 3D visualization of the stress field. In experimental validation on Q235 steel specimens, the system achieved a measurement error of less than ±10 MPa within a stress range of 0 MPa to 150 MPa, with a single-point measurement time under 0.5 seconds. It demonstrated significant advantages in measurement accuracy, efficiency, and ease of operation, enabling high-precision non-destructive testing of stresses in plate components and meeting the requirements for efficiency and reliability in engineering field stress detection.