The anhydrite karst’s area is rare in china, which has been developing in Yanshiping zone of Germud-Lahsa on Qinghai-Tibetan railway. In September 2006, it occurred the land-subsidence at the right shoulder and slope of the railway embankment, about 20 km south from Yanshiping town. In this paper, the geological condition was analyzed in subgrade hazard zone about anhydrite karst, including the characteristics of anhydrite karst growth. By the geologic investigation, the reason of subgrade hazard was summarized, then, the opinion about mending disease was put forward, which can serve as a reference for the similar condition.