A method of constructing an underwater concrete block structure, the method comprising: a first concrete block fabrication step of fabricating a first concrete block comprising a first concrete block body, a column rebar assembly which extends vertically upward from a lower end part thereof connected to the inside of the first concrete block body and protrudes upward from the upper surface of the first concrete block body, and a first watertight packing disposed on the upper surface of the first concrete block body in a form surrounding the column rebar assembly; a guide pole installation step of installing a guide pole on the first concrete block after the first concrete block fabrication step, wherein the guide pole comprises a guide pipe having a shape of a pipe extending vertically tc insert the column rebar assembly along the inside of the guide pipe and a upper insertion guide part formed at the upper end of the guide pipe and having an upwardly tapered shape; a first concrete block installation step of installing the first concrete block underwater after the guide pole installation step; a second concrete block fabrication step of fabricating a second concrete block comprising a second concrete block body having a through hole extending vertically; a second concrete block installation step of installing the second concrete block such that a concrete block assembly is formed by installing the second concrete block on the first concrete block so that the guide pole is inserted into the through hole of the second concrete block after the second concrete block fabrication step and the first concrete block installation step, wherein a concrete-column through hole having a closed lower end is formed in the concrete block assembly by the through hole of the second concrete block and the first concrete block, and the first watertight packing is located between the first concrete block and the second concrete block to prevent water from being introduced into the concrete-column through hole from the outside; a drainage step of removing water contained inside the concrete-column through hole after the second concrete block installation step; a guide pole removal step of removing the guide pole after the drainage step; and a concrete column formation step of forming a concrete column by pouring concrete into the concrete-column through hole after the drainage step, wherein the concrete column comprises the column rebar assembly and the poured concrete integrated with each other and is coupled to the first concrete block body via the column rebar assembly. a first concrete block fabrication step of fabricating a first concrete block comprising a first concrete block body, a column rebar assembly which extends vertically upward from a lower end part thereof connected to the inside of the first concrete block body and protrudes upward from the upper surface of the first concrete block body, and a first watertight packing disposed on the upper surface of the first concrete block body in a form surrounding the column rebar assembly; a guide pole installation step of installing a guide pole on the first concrete block after the first concrete block fabrication step, wherein the guide pole comprises a guide pipe having a shape of a pipe extending vertically tc insert the column rebar assembly along the inside of the guide pipe and a upper insertion guide part formed at the upper end of the guide pipe and having an upwardly tapered shape; a first concrete block installation step of installing the first concrete block underwater after the guide pole installation step; a second concrete block fabrication step of fabricating a second concrete block comprising a second concrete block body having a through hole extending vertically; a second concrete block installation step of installing the second concrete block such that a concrete block assembly is formed by installing the second concrete block on the first concrete block so that the guide pole is inserted into the through hole of the second concrete block after the second concrete block fabrication step and the first concrete block installation step, wherein a concrete-column through hole having a closed lower end is formed in the concrete block assembly by the through hole of the second concrete block and the first concrete block, and the first watertight packing is located between the first concrete block and the second concrete block to prevent water from being introduced into the concrete-column through hole from the outside; a drainage step of removing water contained inside the concrete-column through hole after the second concrete block installation step; a guide pole removal step of removing the guide pole after the drainage step; and a concrete column formation step of forming a concrete column by pouring concrete into the concrete-column through hole after the drainage step, wherein the concrete column comprises the column rebar assembly and the poured concrete integrated with each other and is coupled to the first concrete block body via the column rebar assembly.