Abstract: Wide grading soil has been extensively untilized as impermeable core material ,but so far, little has been done on the study of its property of hydrofracture.This paper describes the achievements of a prelimianarystudy where the wide grading gravelly soil used comes from the high rockfill dam of Pubugou Project,The study shows that:(1)whether the hydrofracture occurs or not mainly depends on the travel content of samle,e.g.it occurs while the gravel content of sample is less that 15%;and (2)the failure pressure uf of hydrofracure increases with the increase of the dry desity of sample,the velocity of water injecting and the confining pressure.