The scanning mode of probes rotating at a high speed can make the ultrasonic testing for steel tubes much more efficient. However, the ultrasonic field produced by a fast rotating probe has a strong time variability, which influences the value of echo signals and leads to a decrease in accuracy of quantitative testing. In order to improve the reliability of quantitative testing, it is necessary to explore how ultrasonic waves travel in steel tubes and establish a mathematical model for the quantitative relation between echo signals and their influencing factors. A following numerical simulation experiment indicates that data from measurement and simulation are consistent with each other. Based on this ultrasonic model, the paper studies the relation between echo signals and relevant parameters in ultrasonic tube testing and claims that this model can optimize parameter configuration in steel tube testing.