Abstract: An experimental method for measuring the stress of accessory is presented in this paper. Based on the acoustoelastic theory, this method can measure the stress from the surface of accessory using critically refracted longitudinal (LCR) wave. According to the relationship between the ultrasonic propagation characteristic and stress condition, a measurement system based on the travel-time is constructed. The "zero-crossing" method is adopted in measuring the travel-time to reduce the errors coursed by character differences of the electronic components. The travel-time of LCR wave is measured by time go digital converter(TDC) with high accuracy.