The invention discloses a ground deformation monitoring device of a building, comprising a dial gauge, a drop ball and a dial gauge supporting device. The drop ball is vertical to the ground; the dial gauge comprises an appointer and a probe that drives the appointer to rotate. The probe leans against a lower end of the drop ball. The dial gauge is mounted on the dial gauge supporting device that is placed on the ground of the building. The invention further discloses an using method of the monitoring device, comprising: suspending the drop ball on the ground; placing the dial gauge supporting device on an upper side of them measuring ground; connecting the dial gauge to the dial gauge supporting device; regulating the dial gauge supporting device to make the dial gauge contact the lower surface of the drop ball in a vertical direction. Using the device is more convenient and accurate to deform the ground in indoor instruction, which avoids kickback such as destroy of the ground that is lifted and sinks in indoor instruction.