A layout optimization model about functional tanks in semi-submersible repair vessels was established under the premise that relevant technologies can be reached. The objective function of this model was put forward under the consideration of three factors about maintenance and repair tanks, such as tank size, tank adjacency, and tank global position. The constraints of this model were set to meet initial metacentric height requirement and guarantee to float on even keel. This optimization model was solved by a two-stage algorithm of combining greedy dropping heuristic algorithm with programming solve. The functional tanks layout solution was obtained with the aid of a semi-submersible hull whose capacity reaches the level of 50 000 tons. This testified the rationality of this model and practicability of this algorithm. And the number of feasible layout solutions shows an upward trend with the increase of the maintenance equipment weight coefficient. This method can improve scientificity in decisionmaking process about functional tanks′ layout in semisubmersible repair vessels.