The invention discloses a liquid metal density measurement device and a liquid metal density measurement method. The liquid metal density measurement device is characterized by comprising a top plate, an upper-end quartz tube, a to-be-tested metal sample, a lower-end quartz tube, a fixed graphite block and a slide block, wherein the top plate, the slide block and the fixed graphite block form a main module; the slide block has a horizontal movable structure between the top plate and the fixed graphite block; the upper-end quartz tube is arranged on the axial position of the slide block; the lower-end quartz tube is arranged in the center of the fixed graphite block along the axial position; in the fixed graphite block, an adjustment ejector rod is arranged below the lower-end quartz tube; and the upper-end quartz tube and the lower-end quartz tube can form a first work station and a second work station under the action of the slide block. According to the invention, the density data with high precision of melt of liquid metal and alloy can be obtained by the measurement device which is easy to operate and convenient in measurement, so that reliable technical support and data support are provided for related theoretical research and engineering application of the liquid metal and alloy.