Abstract: To extend the service life and improve the durability of steel structure materials, a layer of fireproof and anti-corrosion coating is usually applied on the surface of the materials. The quality of the coating directly affects the safety and in-service performance of the components. Therefore, an ultrasonic testing method is proposed to use for quality identification of protective coatings on prefabricated steel structures. Firstly, a coating structure model was established with finite element simulation software to simulate the excitation and reception of coating detection signals, and the reflection characteristics of the coating structure are analyzed. Then, resonance method and pulse reflection method were used to measure the thickness of the coating, and the Discrete Fourier Transform and Hilbert Transform were applied to calculate the coating thickness and the calculated results were compared with the actual thickness. The results show that the relative error of the pulse reflection method in detecting coating thickness is within 3%, which is significantly lower than that of the resonance method. Finally, simulation tests were conducted on different types of defects with pulse reflection method, and the results show that this method can calculate the defect position through A-type detection signals.