A support system for a connection unit for connecting an inner tank and an outer tank of a cryogenic fluid storage tank includes: an inner support formed to surround a part of the connection unit; a head coupled to the inner circumferential surface of a first end portion of the inner support, and formed to comes in contact with an end portion of the connection unit when the connection unit is coupled to the inner support; and an outer support formed to surround the inner support and having a first end portion connected to a second end portion of the inner support, wherein a second end portion of the outer support comes in contact with the inner tank or the outer tank.