The invention discloses a sealing device of a filling packaging machine. The sealing device comprises a bracket, a heat-seal mechanism and a power mechanism and is characterized in that the heat-sealmechanism comprises a heat-seal gland mounting element and at least one pair of heat-seal glands; the heat-seal gland mounting element comprises a left heat-seal gland mounting element and a right heat-seal gland mounting element which can both be arranged on the bracket in a transverse-sliding manner; the pair of heat-seal glands includes a left heat-seal gland and a right heat-seal gland, wherein the left heat-seal gland is fixedly arranged on the left heat-seal gland mounting element, the right heat-seal gland is fixedly arranged on the right heat-seal gland mounting element, and the left heat-seal gland and the right heat-seal gland in one pair correspond to each other; and the power mechanism comprises a left power mechanism and a right power mechanism, wherein the left power mechanism is connected with the left end of the left heat-seal gland mounting element in a transmission manner, and the right power mechanism is connected with the right end of the right heat-seal gland mounting element in a transmission manner. The sealing device has simple structure, high sealing speed and good sealing effect.