Abstract: The GM (1,1) model in the Grey Theory can make a good deal with original deformation measured datas, but it can not deal well with observed objects deformation law prediction with few data. A re-adjustment to affinity coefficient in flat fire was made, and then the unbalanced explicit value was got. Weight of original data series to new data series was discussed. In order to much closer to the deformation values produced by practice deformation law, generated formula of free weights was given.

Key words: Deformation monitoring, Modified GM（1,1）model, Slope