The invention discloses a system and a method for blocking the influence of foundation pit excavation. Before foundation pit excavation, a steel plate is vertically pressed in the middle of a foundation pit and a building; four circular holes are drilled in the steel plate; two sides of the circular holes are covered by elastic films; a grouting pipe is embedded in the steel plate; the grouting pipe is connected with the four circular holes, and simultaneously connected with a valve at the top of the steel plate; the valve is connected with a water pipe; the water pipe is connected with one side of a pump; the other side of the pump is connected with the water pipe; a mud pit is excavated around the steel plate; the water pipe extends into the mud pit; an optical fiber test component is buried on one side of the steel plate close to the building; the optical fiber test component is connected with a conducting wire; the conducting wire is connected with a controller; and the controlleris connected with the pump. The controller can control the operation of the pump according to the pressure value measured by the optical fiber test component.