The invention relates to a method for preparing a graphite nano sheet, in particular to a method for preparing a graphite nano sheet by utilizing the high energy ball grinding. The method is characterized in that the method comprises the following steps that: (1) according to the mol ratio of a soluble powder grinding body to expandable graphite of between 1:1 and 8:1, the soluble powder grinding body and the expandable graphite are weighed up for later use; (2) the soluble powder grinding bodyand the expandable graphite are put in a grinding cylinder, and added with grinding balls according to a ball to material mass ratio of between 2:1 and 10:1, and subjected to ball grinding at the rotary speed of between 350 and 580 rev./m for 4 to 8h, and the ball grinding products and the grinding balls are taken out of the ball grinding cylinder; (4) the soluble powder grinding body in the ball grinding products obtained from the step(3) is completely dissolved or completely reacted to become soluble salt by using solvents and washed by distilled water for 2 to 6 times, and solids and liquids are separated; and finally, the solids are obtained by separation and dried so as to obtain the graphite nano sheet. The method has the advantages of simple process, low cost, no environmental pollution and the realization of mass industrial production.