The foundation pit of Songshanhu Metro station on DongganHuizhou railway transit line has to be enlarged due to the modification of the design, therefore the steel supports have to be replaced. The forcing system of the foundation pit will change a lot during the replacing of the steel supports. The forcing system of the foundation pit is numerically analyzed by means of Lizheng software and the scheme of the enlarging and supportreplacing of the foundation pit is established. The construction safety is guaranteed by carrying out theoretical analysis, key construction technology control and foundation pit monitoring.