Abstract: This paper aims to use ultrasonic surface waves to detect the rail tread crack. A group of specimens with different depth were designed and produced. The test was carried out by the imaging method of B scan along the vertical side of rail by 0.5 MHz surface wave probe. In order to decrease the disadvantage of low resolution that caused by multimodes, this paper used shift superimposed technique for different place of A scan wave by data processing software. This method could achieve accurate position of the cracks and also could reflect the depth of the crack.