This paper brought forward a data packing method of incomplete information system based on rough sets and grey system theory. This method takes advantage of the lower approximation in rough sets to do the first data packing, and then, according to the value-taking probability of the attribute value, finds the result to do the second packing, thus accomplishes the completion of incomplete information system. This method can adequately reflect the rules and avoid the conflict in information system. When the data in information system and the lost data are evenly distributed, the packing data can reflect the true situation of information system.