Abstract: HSS roll is widely used in the steel manufactory because of its nice performance. But the detecting work on the roll surface is normally done by hand. The efficiency is too low, and the work is too hard by this way. Furthermore, some small cracks may be skipped over. In order to solve this problem, Baosteel company imported a surface wave detector from KRAUTKRAMER company in Japan, which was installed on the roll grinder and was used for detecting the HSS roll automatically. The paper introduces the principle of the KRAUTKRAMER surface wave detector, and introduces the inspection map of the ultrasonic surface wave detector. The paper also summarizes a new detect criterion for the HSS roll.