The fish propagation program that produces fish to be released into natural bodies of water is dramatically increasing. The swimming crab Portunus trituberculatus is one of the most valuable species for fisheries. The simulation model was constructed to evaluate the optimal stocking strategy for the swimming crab. The simulation process was formed by the six components, the swimming crab, the prey of the crab Musculus senhousia, two competitors (Portunus sanguinolentus and Charybdis japonica),and two predators (the gobies and the hermit crabs). The population growth of the mussel was assumed to obey the logistic equation. The crabs decreased by natural mortality (competition, predation, and cannibalism)and fishing, but increased by reproduction and releasing juveniles. The results of our simulation showed that the exists an optimal day to release the crabs in order to get the maximum catch in weight. The crabs grew larger when they were released early in the year. In combination with the releasing day and number, we could get the optimal day for the target catch amount. © 1995, The Japanese Society of Fisheries Science. All rights reserved.