Using the fractal theory， the preparation method on the scale sample with same fractal dimension of the in-site filling material produced by ball mill was studied. Based on the requirements of simulating the in-site repetitive crush mechanism， the ball mill was selected to prepare the scale sample. The effects of the experimental influence parameters such as the number of rotation， number of steel balls and initial particles size on the goodness of the fractal simulation and fractal dimensions were investigated by using the orthogonal tests. The effect of secondary crushing on the filling material during the preparation of middle Triaxial specimen was further examined. The results show that with the following crushing parameters: the number of ball mill rotation is 100 rad， the number of steel ball is 9， the initial particle size of the rock is 20mm， the middle Triaxial specimen scale sample with the same fractal dimension as the in-site filling material can be prepared.