The invention provides a compact liquid metal battery and an assembly method thereof. The battery includes a negative column, a high temperature sealing device, a negative current collector, a battery top cover, a battery shell, a battery bottom cover, a negative material, an electrolyte material and a positive material. The battery top cover, the battery shell and the battery bottom cover are in seal connection and form a sealed cavity. The negative material, the electrolyte material and the positive material are all arranged in the sealed cavity. The negative column passes through the battery top cover, and is in seal connection with the battery top cover through the high temperature sealing device. One negative column end stretching into the sealed cavity is connected to the negative current collector. The negative column body stretching into the sealed cavity is equipped with a round table. The high temperature sealing device includes a sealing gasket, a sealing gum layer, an insulation spacer and a fastening nut that are sleeved on the negative column. The sealing gasket is compressed between the round table and the battery top cover, the sealing gum layer seals and fills the space between the battery top cover and the negative column, and the insulation spacer is compressed on the battery top cover through the fastening nut.