The invention relates to a pipe joint immersing ballast water system, particularly to a ballast water system which achieves stable and rapid pipe joint immersion by controlling water storage of a ballast water tank. The pipe joint immersing ballast water system comprises a pipe joint control circuit, the ballast water tank and a ballast pump, wherein the ballast pump is connected with the ballast water tank through pipes. According to the pipe joint immersing ballast water system, by means of the design of the ballast water tank and according to the buoyancy principle, the dead weight of a pipe joint can be controlled by injecting water into or draining water out of the ballast water tank to adapt to buoyancy at different depths under the seat, so that rapid, smooth and stable pipe joint immersion can be achieved, the immersing speed of the pipe joint can be matched with the descending and hoisting of sling cables, the load of the sling cables can be reduced, the immersion working precision can be enhanced, the immersion working speed can be increased, and the immersion working efficiency can be improved.