The invention discloses underwater excavation system construction of a sand pump vessel guided and located by steel ropes. The underwater excavation system construction is characterized in that the system is composed of a locating steel rope (1) with two ends fixed to banks, a sand pump vessel capable of pumping sand and excavating underwater and a capstan (2) connected with the locating steel rope and fixed on the sand pump vessel body. When the sand pump vessel pumps sand and excavates, the sand pump vessel moves in parallel and is locked along guidance of the steel rope, a sand pump halter (4) connected with a sand pump tube on the vessel can pump sand and excavate within a scope sideline (6) which the sand pump halter can move to. The excavation system can be combined in a plurality of modes to satisfy different conditions on site, the system can be composed of one sand pump vessel guided and located by one steel rope or a plurality of sand pump vessels guided and located by a plurality of steel ropes according to factors such as the size and the number of the sand pump vessels, the movement scope of halters on the vessel and the time limit for a project. The system can be flexibly combined and easy to operate, the vessel can be truly fixed underwater, less excavation, missing excavation and repeat excavation can be effectively avoided, and the efficiency of excavation can be greatly raised.