Due to long-term contact with crude oil and other media, tank bottom is prone to corrosion, resulting in crude oil leakage and structural failure. Ultrasonic thickness measurement can detect the corrosion of the bottom plate in time and reduce the risk of accidents. In this paper, an ultrasonic thickness measuring system is used to measure the thickness of tank bottom plate. Firstly, the principle of ultrasonic thickness measurement is discussed, based on which the hardware system is designed. Finally, indoor and outdoor experiments were carried out. The experimental results show that the wall thickness measurement accuracy is better than 0.1 mm and the received signal consistency is good for 8–40 mm carbon steel plate without solid sediment. It shows that the system can be applied to the thickness measurement of tank bottom plate, and has the advantages of high efficiency, high precision, good consistency, and non-destructive.