Abstract: Mechanical properties of diamond wire saw under the action of ultrasonic vibration were studied.The vibration system and connection device were self-designed, and the uniaxial tensile tests were carried out for different diameters of diamond wire saw by use of the ultrasonic vibration system in an attempt to find the changes in mechanical properties of diamond wire saw under different frequencies and different amplitudes.Diamond wire saw crack growth mechanism and softening mechanism under the condition of ultrasonic tension were studied.Wire saw fracture morphology were analyzed using electron metallographic microscope with or without ultrasonic vibration.Resultsshowed that the alternating stresses of wire saw were generated under the action of ultrasonic vibration, and that there appeared micro-cracks, which rapidly expanded and teared.High frequency vibration produced localized high temperature and accelerated diffusion process, which eventually developed into a macro defect.When the ultrasonic stretching frequency was loaded to 20 kHz, the crack growth rate could reach 10^-9~10^-8 mm/cycle.