Abstract: There are many chinks in the Huai River Dike as the result of the coal mining under the Huai River. It is consindered generaly that those chinks in the Dike could have a great threat to the security of the Dike and the coal mining under the River. In this paper, the chink's forming condition and it's growth depths were analysed and demonstrated bosed on the study on the soil mass engineering geological properties as well as by the means of testing and mechanics analysis method, several important conclusions obtained show as:1. about the preseat Huai River Dike in Huainan, when the tensile strain of the clay Dike exceeds 8-12mm/m and the sand Dike's exceeds 3-5mm/m,the chinks in the Dike body will arise; 2. the chink's growth depth will not ever exceed a certain limit value, this value deals with the machanical characteristics of the soil mass, at present, the mining chink's limit depth of the Huai River Dike in Huainan is approximatly 4.0 meters for the clay Dike and 2.0 meters for the sand Dike; 3. only to adopt clayey grouting and to pave the facing water slope with a kind of unpermeable plastic film and so on measures, the existence of the Dike's chinks will not threaten the security of the coal mining under the River and the Large Dike's self.