Disclosed is a construction method of a foundation for an underwater support structure, which is capable of rapidly installing the foundation of a large-scale structure on a sea floor, and also sufficiently ensuring a horizontal load supporting capability. The construction method includes installing a pile having a head part, in which a catching groove is formed, in a sea floor G; fabricating the foundation for the underwater support structure, in which a buried guide tube is formed to protrude downwardly from a lower surface of the foundation for an underwater support structure, and settling the foundation for the underwater support structure on the sea floor, such that the head part of the pile is inserted into the guide tube; and anchoring the pile into the guide tube using an elastically protruding settlement device formed in the guide tube.