ROUSTIDA algorithm is used to data completing in rough set for incomplete information systems, however its coverage is not good enough. To solve the problem, an improved algorithm is proposed from the angle of group decision. Direction-area of attributes on columns and simple-majority-rule ratio of objects on rows of decision table is defined respectively, and they are combined with ROUSTIDA algorithm, thus the coverage of improved algorithm surpasses that of original algorithm, and the problems of multimode or no mode are avoided. The result of an instance shows the availability of proposed algorithm.