Because of the high-speed, high transport capacity, low power consumption and a lot of technical and economic advantages, high-speed rail way are universal importance. High-speed railway with the speed of more than 300k/h has been run in China. But fatigue cracking of wleded bogie structure is markedly increased with increasing the train speed. How to avoid fatigue destroy of wleded bogie structure and ensure the safety of transportation are urgent problems to be soved in engineering. A lot of research works have been done at home and abroad. Comparing with traditional surface engineering method, there are many advantages of ultrasonic impact , for example, simple operation, less power consumption, high efficiency, adapt to a wide range, easy to achieve automate production and so on. It is an effective way to surface strengthening of metallic materials. Plastic flow and grain refinement on the metal surface can be obtained by using ultrasonic impact method, and the residual compressive stress on the surface can also be formed. So the mechanical properties of metal surface can be greatly improved. It is new method used in the area of welded structure, especially in the welded bogie structure. It is a new research direction to research the surface nanocrystallization mechanisium of ultrasonic impact, the effect of ultrasonic impac on the fatigue properties and failure mechanisium of wled joint of bogie.