Abstract: Block B125 in Gucheng oilfield is ordinary heavy oil reservoirs of type 12 with the characteristics of shallow depth, small thickness and serious lateral and vertical heterogeneity. Huff and puff recovery was replaced by wa-terflooding in this block in 1996, Water channeling was serious in some wells and water cut went up to over 90%. In view of the geological characteristics, a formula for profile correction agent was selected in 2001 through experiments. It has the advantages of large gel strength, good thermal stability, a plugging ratio over 80% and controllable gel forming time. Application in 3 wells show that the water channels are effectively plugged and oil output increase while water cut decrease.