Abstract: The checked concrete strength of R.C.single foundations under columns is less than C10 in case of a steel structural factory that is under construction.The composite structure of steel and R.C.is used to strengthen the R.C. single foundations,which makes their strength meet the requirements.Based on different forced features,two schemes are designed to strengthen side and middle columns.The methods and orders of construction are discussed.The strengthened R.C.single foundation have enough strength and economic benefit.The design and construction schemes may be a reference for the same kind project.