Abstract: Based on study of fundamental features karstic collapse column of in Liuqiao NO.1 coal mine,and some of mine in other region,it is concluded that the rock mechanics conditions consist of the following aspects :lst,the collapse column are almost contribued over an area of extensional tectonics or self-weight street field;2nd,its rock stucture is easy to fall;3rd,its stress state of cave-in is similar to the roof fall caused by mining;4th,the essential factor of the column growing up is sustained karstification