<p>Accurately detecting the axial stress of bolts is of significant importance for the safety and reliability of the entire equipment or structure. In response to the problems of low accuracy in measuring bolt stress using conventional stress detection methods and difficulty in experimental calibration using ultrasonic stress detection methods, this paper proposes an ultrasonic detection method of bolt axial stress based on simulation calibration. Firstly, a mathematical model of the relationship between axial stress and the time-of-flight (TOF) of ultrasonic waves inside the bolt is derived based on the acoustic elastic theory and Hooke’s law, and the calculation method for TOF is provided. Then, a finite element model is used to investigate the propagation characteristics of ultrasonic waves inside the bolt and perform stress calibration simulations to establish the functional relationship between stress and TOF. Finally, a hardware and software platform for bolt axial stress detection is built using self-developed equipment. The TOF of ultrasonic waves in bolts under different stress states is measured, and the calculated axial stress of the bolt is obtained by incorporating the TOF difference into the established functional relationship. When the bolt axial stress exceeds 100&#xa0;MPa, the relative error between the stress indirectly measured by the ultrasonic detection method of bolt axial stress based on simulation calibration and the stress directly measured using strain gauges is as low as 4.25%, confirming the effectiveness and feasibility of the method.</p>