The monitoring and evaluation of the corrosion condition of the storage tank floor provides a strong guarantee for preventing the occurrence of dangerous accidents, providing support for predicting the service life of the storage tank floor, and provides a basis for scientific management and decision-making. The complexity of the floor structure and the attenuation characteristics of the guide wave make it difficult for the existing guide technology to evaluate the corrosion state of the bottom plate of large storage tanks. This paper studies the principle of excitation and signal reception of ultrasonic guide waves, and the characteristics of reflection and transmission signals after corrosion defects and the detection principle of ultrasonic nonlinear characteristics, analyzes the changes of received signals in different propagation paths, extracts the time field domain and frequency domain information in the difference signal, establishes the relationship model between characteristic parameters and corrosion depth, and finally obtains the classification method for the corrosion status evaluation of typical corrosion defects such as rectangular, circle and cone. The test results show that it can accurately determine whether the tank floor has corrosion defect and quantitatively determine the depth state of corrosion defect.