The effect of filled ratio on flow characteristics of grinding media was investigated for a horizontal type sand mill, in which the internal blade and external cylinder counter rotated independently. The relationship between flow characteristics and grinding performance was discussed by earring out grinding tests of calcium carbonate. As a result, it was found that the grinding characteristics obtained for both rotation methods can be well correlated as a function of intensity of velocity fluctuations weighted by appearance frequency and the second power of filled ratio, where the reciprocal collision probability of media particles is taken into consideration.