Abstract: Use the "DC4 Ultrasonic Detector" to detect the aluminum plate embedded with gypsum, with an unknown distribution of the velocity of the longitudinal wave, and collect "arrival time" data along each ray. Radon transform (line integral) is done on rays along the unknown digital image, with the same ray arrangement each ray's integral step is constant, thus easy to set up a linear algebraic equations of the unknown digital image. Use "Algebraic Reconstruction Technique" addition modified iteration to compile R program, with this program to handle the "arrival time vector" data and reconstruct the unknown digital image. The necessary and sufficient conditions, the test conditions and the inspection method for identifying the gypsum hole are proposed to identify the location of the gypsum hole on the aluminum plate mode based on the reconstructed digital image. In addition, the "Three-plate plane model" was tested and analyzed according to the same treatment method for the aluminum plate mode. The results of image reconstruction in this paper have reference value for understanding CT imaging methods and contribute to the popularization and application of CT imaging technology.