The liquid cargo replenishment decision based on ship’s stability, strength and the floating state is a multiobjective
optimization problem. The mathematical model of multi-objective is built in this paper. Aiming to obtain the
feasible solution, the adaptive step ergodic of permutation and combination is applied in terms of the cargo oil tank and
the water ballast tank. particle swarm optimization (PSO) algorithm is applied into the project. On the basis of constraint
conditions, the multi-objective optimization function is proved and take it into real operating mode for calculation and
analysis. Improved objective function that is built based on multi-objective mathematical model. Taking real calculation
example to verify the effectiveness of improved function and PSO algorithm. The result is good and the time complexity
and mathematical precision are both improved effectively.