Ultrasonic polar scan (UPS) records the amplitude in transmission for a wide range of incidence angles, providing a UPS image with characteristic contours reflecting the acoustic parameters of the material. This study focused on a newly developed wave velocity measurement of the DD6 single-crystal material plate by analyzing the UPS image to realize the ultrasonic thickness measurement of the DD6 single-crystal material plate accordingly. Firstly, considering transducer contour size compensation, the UPS images are obtained by numerical simulation on the DD6 single-crystal material plates with different crystal orientations. Secondly, the fitting equations are obtained by analyzing the UPS images to calculate wave velocity in the thickness direction. Finally, a 5-joint UPS scanner is designed to validate the accuracy of wave velocity simulation results experimentally, and it indicates a good agreement with conventional ultrasonic velocity measurement. The measurement results demonstrated that the UPS method could evaluate the wave velocity in the through-thickness direction of the DD6 single-crystal material plate with high precision.