Recently, composite particles have been used in various fields, and their structure control is required. Then, the uniformity of surface of individual fine particles coated by rotational impact blending is to be paid attention as the microstructure. In this research, uniformity is evaluated by the distance distribution of the nearest fine particles on the coated particle surface and the relationship among the operation conditions is investigated. As a result, the uniformity enhanced with the increase in the peripheral velocity of the rotor blade, the coarse particle diameter and the treatment time and with decrease in the fine particle diameter. The empirical formula of the uniformity is obtained from the operational conditions. In reality, fine particles are coated to be overlapped occasionally and its ratio was correlated with the uniformity. It, therefore, becomes possible to prepare coated fine particles of required coating ratio and uniformity.